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nest-open-source / manifest_repos / toolchain / 6143c57c644e0da7c4a10d1b4af322f92e74e6f7 / . / arm / usr / lib / rustlib / src / rust / library / core / src / fmt / mod.rs
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//! Utilities for formatting and printing strings.
#![stable(feature = "rust1", since = "1.0.0")]
use crate::cell::{Cell, Ref, RefCell, RefMut, SyncUnsafeCell, UnsafeCell};
use crate::char::EscapeDebugExtArgs;
use crate::iter;
use crate::marker::PhantomData;
use crate::mem;
use crate::num::fmt as numfmt;
use crate::ops::Deref;
use crate::result;
use crate::str;
mod builders;
#[cfg(not(no_fp_fmt_parse))]
mod float;
#[cfg(no_fp_fmt_parse)]
mod nofloat;
mod num;
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "Alignment")]
/// Possible alignments returned by `Formatter::align`
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Alignment {
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be left-aligned.
Left,
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be right-aligned.
Right,
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be center-aligned.
Center,
}
#[stable(feature = "debug_builders", since = "1.2.0")]
pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[doc(hidden)]
pub mod rt {
pub mod v1;
}
/// The type returned by formatter methods.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// #[derive(Debug)]
/// struct Triangle {
/// a: f32,
/// b: f32,
/// c: f32
/// }
///
/// impl fmt::Display for Triangle {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {}, {})", self.a, self.b, self.c)
/// }
/// }
///
/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
///
/// assert_eq!(format!("{pythagorean_triple}"), "(3, 4, 5)");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub type Result = result::Result<(), Error>;
/// The error type which is returned from formatting a message into a stream.
///
/// This type does not support transmission of an error other than that an error
/// occurred. Any extra information must be arranged to be transmitted through
/// some other means.
///
/// An important thing to remember is that the type `fmt::Error` should not be
/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
/// have in scope.
///
/// [`std::io::Error`]: ../../std/io/struct.Error.html
/// [`std::error::Error`]: ../../std/error/trait.Error.html
///
/// # Examples
///
/// ```rust
/// use std::fmt::{self, write};
///
/// let mut output = String::new();
/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
/// panic!("An error occurred");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Error;
/// A trait for writing or formatting into Unicode-accepting buffers or streams.
///
/// This trait only accepts UTF-8–encoded data and is not [flushable]. If you only
/// want to accept Unicode and you don't need flushing, you should implement this trait;
/// otherwise you should implement [`std::io::Write`].
///
/// [`std::io::Write`]: ../../std/io/trait.Write.html
/// [flushable]: ../../std/io/trait.Write.html#tymethod.flush
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Write {
/// Writes a string slice into this writer, returning whether the write
/// succeeded.
///
/// This method can only succeed if the entire string slice was successfully
/// written, and this method will not return until all data has been
/// written or an error occurs.
///
/// # Errors
///
/// This function will return an instance of [`Error`] on error.
///
/// The purpose of std::fmt::Error is to abort the formatting operation when the underlying
/// destination encounters some error preventing it from accepting more text; it should
/// generally be propagated rather than handled, at least when implementing formatting traits.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
/// f.write_str(s)
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, "hola").unwrap();
/// assert_eq!(&buf, "hola");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn write_str(&mut self, s: &str) -> Result;
/// Writes a [`char`] into this writer, returning whether the write succeeded.
///
/// A single [`char`] may be encoded as more than one byte.
/// This method can only succeed if the entire byte sequence was successfully
/// written, and this method will not return until all data has been
/// written or an error occurs.
///
/// # Errors
///
/// This function will return an instance of [`Error`] on error.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
/// f.write_char(c)
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, 'a').unwrap();
/// writer(&mut buf, 'b').unwrap();
/// assert_eq!(&buf, "ab");
/// ```
#[stable(feature = "fmt_write_char", since = "1.1.0")]
fn write_char(&mut self, c: char) -> Result {
self.write_str(c.encode_utf8(&mut [0; 4]))
}
/// Glue for usage of the [`write!`] macro with implementors of this trait.
///
/// This method should generally not be invoked manually, but rather through
/// the [`write!`] macro itself.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
/// f.write_fmt(format_args!("{s}"))
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, "world").unwrap();
/// assert_eq!(&buf, "world");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result {
write(&mut self, args)
}
}
#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
impl<W: Write + ?Sized> Write for &mut W {
fn write_str(&mut self, s: &str) -> Result {
(**self).write_str(s)
}
fn write_char(&mut self, c: char) -> Result {
(**self).write_char(c)
}
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
(**self).write_fmt(args)
}
}
/// Configuration for formatting.
///
/// A `Formatter` represents various options related to formatting. Users do not
/// construct `Formatter`s directly; a mutable reference to one is passed to
/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
///
/// To interact with a `Formatter`, you'll call various methods to change the
/// various options related to formatting. For examples, please see the
/// documentation of the methods defined on `Formatter` below.
#[allow(missing_debug_implementations)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Formatter<'a> {
flags: u32,
fill: char,
align: rt::v1::Alignment,
width: Option<usize>,
precision: Option<usize>,
buf: &'a mut (dyn Write + 'a),
}
impl<'a> Formatter<'a> {
/// Creates a new formatter with default settings.
///
/// This can be used as a micro-optimization in cases where a full `Arguments`
/// structure (as created by `format_args!`) is not necessary; `Arguments`
/// is a little more expensive to use in simple formatting scenarios.
///
/// Currently not intended for use outside of the standard library.
#[unstable(feature = "fmt_internals", reason = "internal to standard library", issue = "none")]
#[doc(hidden)]
pub fn new(buf: &'a mut (dyn Write + 'a)) -> Formatter<'a> {
Formatter {
flags: 0,
fill: ' ',
align: rt::v1::Alignment::Unknown,
width: None,
precision: None,
buf,
}
}
}
// NB. Argument is essentially an optimized partially applied formatting function,
// equivalent to `exists T.(&T, fn(&T, &mut Formatter<'_>) -> Result`.
extern "C" {
type Opaque;
}
/// This struct represents the generic "argument" which is taken by the Xprintf
/// family of functions. It contains a function to format the given value. At
/// compile time it is ensured that the function and the value have the correct
/// types, and then this struct is used to canonicalize arguments to one type.
#[derive(Copy, Clone)]
#[allow(missing_debug_implementations)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[doc(hidden)]
pub struct ArgumentV1<'a> {
value: &'a Opaque,
formatter: fn(&Opaque, &mut Formatter<'_>) -> Result,
}
/// This struct represents the unsafety of constructing an `Arguments`.
/// It exists, rather than an unsafe function, in order to simplify the expansion
/// of `format_args!(..)` and reduce the scope of the `unsafe` block.
#[allow(missing_debug_implementations)]
#[doc(hidden)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
pub struct UnsafeArg {
_private: (),
}
impl UnsafeArg {
/// See documentation where `UnsafeArg` is required to know when it is safe to
/// create and use `UnsafeArg`.
#[doc(hidden)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[inline(always)]
pub unsafe fn new() -> Self {
Self { _private: () }
}
}
// This guarantees a single stable value for the function pointer associated with
// indices/counts in the formatting infrastructure.
//
// Note that a function defined as such would not be correct as functions are
// always tagged unnamed_addr with the current lowering to LLVM IR, so their
// address is not considered important to LLVM and as such the as_usize cast
// could have been miscompiled. In practice, we never call as_usize on non-usize
// containing data (as a matter of static generation of the formatting
// arguments), so this is merely an additional check.
//
// We primarily want to ensure that the function pointer at `USIZE_MARKER` has
// an address corresponding *only* to functions that also take `&usize` as their
// first argument. The read_volatile here ensures that we can safely ready out a
// usize from the passed reference and that this address does not point at a
// non-usize taking function.
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
static USIZE_MARKER: fn(&usize, &mut Formatter<'_>) -> Result = |ptr, _| {
// SAFETY: ptr is a reference
let _v: usize = unsafe { crate::ptr::read_volatile(ptr) };
loop {}
};
macro_rules! arg_new {
($f: ident, $t: ident) => {
#[doc(hidden)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[inline]
pub fn $f<'b, T: $t>(x: &'b T) -> ArgumentV1<'_> {
Self::new(x, $t::fmt)
}
};
}
#[rustc_diagnostic_item = "ArgumentV1Methods"]
impl<'a> ArgumentV1<'a> {
#[doc(hidden)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[inline]
pub fn new<'b, T>(x: &'b T, f: fn(&T, &mut Formatter<'_>) -> Result) -> ArgumentV1<'b> {
// SAFETY: `mem::transmute(x)` is safe because
// 1. `&'b T` keeps the lifetime it originated with `'b`
// (so as to not have an unbounded lifetime)
// 2. `&'b T` and `&'b Opaque` have the same memory layout
// (when `T` is `Sized`, as it is here)
// `mem::transmute(f)` is safe since `fn(&T, &mut Formatter<'_>) -> Result`
// and `fn(&Opaque, &mut Formatter<'_>) -> Result` have the same ABI
// (as long as `T` is `Sized`)
unsafe { ArgumentV1 { formatter: mem::transmute(f), value: mem::transmute(x) } }
}
arg_new!(new_display, Display);
arg_new!(new_debug, Debug);
arg_new!(new_octal, Octal);
arg_new!(new_lower_hex, LowerHex);
arg_new!(new_upper_hex, UpperHex);
arg_new!(new_pointer, Pointer);
arg_new!(new_binary, Binary);
arg_new!(new_lower_exp, LowerExp);
arg_new!(new_upper_exp, UpperExp);
#[doc(hidden)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
pub fn from_usize(x: &usize) -> ArgumentV1<'_> {
ArgumentV1::new(x, USIZE_MARKER)
}
fn as_usize(&self) -> Option<usize> {
// We are type punning a bit here: USIZE_MARKER only takes an &usize but
// formatter takes an &Opaque. Rust understandably doesn't think we should compare
// the function pointers if they don't have the same signature, so we cast to
// usizes to tell it that we just want to compare addresses.
if self.formatter as usize == USIZE_MARKER as usize {
// SAFETY: The `formatter` field is only set to USIZE_MARKER if
// the value is a usize, so this is safe
Some(unsafe { *(self.value as *const _ as *const usize) })
} else {
None
}
}
}
// flags available in the v1 format of format_args
#[derive(Copy, Clone)]
enum FlagV1 {
SignPlus,
SignMinus,
Alternate,
SignAwareZeroPad,
DebugLowerHex,
DebugUpperHex,
}
impl<'a> Arguments<'a> {
/// When using the format_args!() macro, this function is used to generate the
/// Arguments structure.
#[doc(hidden)]
#[inline]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
pub const fn new_v1(pieces: &'a [&'static str], args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
if pieces.len() < args.len() || pieces.len() > args.len() + 1 {
panic!("invalid args");
}
Arguments { pieces, fmt: None, args }
}
/// This function is used to specify nonstandard formatting parameters.
///
/// An `UnsafeArg` is required because the following invariants must be held
/// in order for this function to be safe:
/// 1. The `pieces` slice must be at least as long as `fmt`.
/// 2. Every [`rt::v1::Argument::position`] value within `fmt` must be a
/// valid index of `args`.
/// 3. Every [`Count::Param`] within `fmt` must contain a valid index of
/// `args`.
#[doc(hidden)]
#[inline]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
#[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
pub const fn new_v1_formatted(
pieces: &'a [&'static str],
args: &'a [ArgumentV1<'a>],
fmt: &'a [rt::v1::Argument],
_unsafe_arg: UnsafeArg,
) -> Arguments<'a> {
Arguments { pieces, fmt: Some(fmt), args }
}
/// Estimates the length of the formatted text.
///
/// This is intended to be used for setting initial `String` capacity
/// when using `format!`. Note: this is neither the lower nor upper bound.
#[doc(hidden)]
#[inline]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
pub fn estimated_capacity(&self) -> usize {
let pieces_length: usize = self.pieces.iter().map(|x| x.len()).sum();
if self.args.is_empty() {
pieces_length
} else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
// If the format string starts with an argument,
// don't preallocate anything, unless length
// of pieces is significant.
0
} else {
// There are some arguments, so any additional push
// will reallocate the string. To avoid that,
// we're "pre-doubling" the capacity here.
pieces_length.checked_mul(2).unwrap_or(0)
}
}
}
/// This structure represents a safely precompiled version of a format string
/// and its arguments. This cannot be generated at runtime because it cannot
/// safely be done, so no constructors are given and the fields are private
/// to prevent modification.
///
/// The [`format_args!`] macro will safely create an instance of this structure.
/// The macro validates the format string at compile-time so usage of the
/// [`write()`] and [`format()`] functions can be safely performed.
///
/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
/// and `Display` contexts as seen below. The example also shows that `Debug`
/// and `Display` format to the same thing: the interpolated format string
/// in `format_args!`.
///
/// ```rust
/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
/// assert_eq!("1 foo 2", display);
/// assert_eq!(display, debug);
/// ```
///
/// [`format()`]: ../../std/fmt/fn.format.html
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "Arguments")]
#[derive(Copy, Clone)]
pub struct Arguments<'a> {
// Format string pieces to print.
pieces: &'a [&'static str],
// Placeholder specs, or `None` if all specs are default (as in "{}{}").
fmt: Option<&'a [rt::v1::Argument]>,
// Dynamic arguments for interpolation, to be interleaved with string
// pieces. (Every argument is preceded by a string piece.)
args: &'a [ArgumentV1<'a>],
}
impl<'a> Arguments<'a> {
/// Get the formatted string, if it has no arguments to be formatted.
///
/// This can be used to avoid allocations in the most trivial case.
///
/// # Examples
///
/// ```rust
/// use std::fmt::Arguments;
///
/// fn write_str(_: &str) { /* ... */ }
///
/// fn write_fmt(args: &Arguments) {
/// if let Some(s) = args.as_str() {
/// write_str(s)
/// } else {
/// write_str(&args.to_string());
/// }
/// }
/// ```
///
/// ```rust
/// assert_eq!(format_args!("hello").as_str(), Some("hello"));
/// assert_eq!(format_args!("").as_str(), Some(""));
/// assert_eq!(format_args!("{}", 1).as_str(), None);
/// ```
#[stable(feature = "fmt_as_str", since = "1.52.0")]
#[rustc_const_unstable(feature = "const_arguments_as_str", issue = "103900")]
#[must_use]
#[inline]
pub const fn as_str(&self) -> Option<&'static str> {
match (self.pieces, self.args) {
([], []) => Some(""),
([s], []) => Some(s),
_ => None,
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for Arguments<'_> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
Display::fmt(self, fmt)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Arguments<'_> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
write(fmt.buf, *self)
}
}
/// `?` formatting.
///
/// `Debug` should format the output in a programmer-facing, debugging context.
///
/// Generally speaking, you should just `derive` a `Debug` implementation.
///
/// When used with the alternate format specifier `#?`, the output is pretty-printed.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
/// comma-separated list of each field's name and `Debug` value, then `}`. For
/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
/// `Debug` values of the fields, then `)`.
///
/// # Stability
///
/// Derived `Debug` formats are not stable, and so may change with future Rust
/// versions. Additionally, `Debug` implementations of types provided by the
/// standard library (`libstd`, `libcore`, `liballoc`, etc.) are not stable, and
/// may also change with future Rust versions.
///
/// # Examples
///
/// Deriving an implementation:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
/// ```
///
/// Manually implementing:
///
/// ```
/// use std::fmt;
///
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// impl fmt::Debug for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// f.debug_struct("Point")
/// .field("x", &self.x)
/// .field("y", &self.y)
/// .finish()
/// }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
/// ```
///
/// There are a number of helper methods on the [`Formatter`] struct to help you with manual
/// implementations, such as [`debug_struct`].
///
/// [`debug_struct`]: Formatter::debug_struct
///
/// Types that do not wish to use the standard suite of debug representations
/// provided by the `Formatter` trait (`debug_struct`, `debug_tuple`,
/// `debug_list`, `debug_set`, `debug_map`) can do something totally custom by
/// manually writing an arbitrary representation to the `Formatter`.
///
/// ```
/// # use std::fmt;
/// # struct Point {
/// # x: i32,
/// # y: i32,
/// # }
/// #
/// impl fmt::Debug for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "Point [{} {}]", self.x, self.y)
/// }
/// }
/// ```
///
/// `Debug` implementations using either `derive` or the debug builder API
/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
///
/// Pretty-printing with `#?`:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(format!("The origin is: {origin:#?}"),
/// "The origin is: Point {
/// x: 0,
/// y: 0,
/// }");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented(
on(
crate_local,
label = "`{Self}` cannot be formatted using `{{:?}}`",
note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {Debug} for {Self}`"
),
message = "`{Self}` doesn't implement `{Debug}`",
label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`"
)]
#[doc(alias = "{:?}")]
#[rustc_diagnostic_item = "Debug"]
#[rustc_trivial_field_reads]
pub trait Debug {
/// Formats the value using the given formatter.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Position {
/// longitude: f32,
/// latitude: f32,
/// }
///
/// impl fmt::Debug for Position {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// f.debug_tuple("")
/// .field(&self.longitude)
/// .field(&self.latitude)
/// .finish()
/// }
/// }
///
/// let position = Position { longitude: 1.987, latitude: 2.983 };
/// assert_eq!(format!("{position:?}"), "(1.987, 2.983)");
///
/// assert_eq!(format!("{position:#?}"), "(
/// 1.987,
/// 2.983,
/// )");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
pub(crate) mod macros {
/// Derive macro generating an impl of the trait `Debug`.
#[rustc_builtin_macro]
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
pub macro Debug($item:item) {
/* compiler built-in */
}
}
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[doc(inline)]
pub use macros::Debug;
/// Format trait for an empty format, `{}`.
///
/// Implementing this trait for a type will automatically implement the
/// [`ToString`][tostring] trait for the type, allowing the usage
/// of the [`.to_string()`][tostring_function] method. Prefer implementing
/// the `Display` trait for a type, rather than [`ToString`][tostring].
///
/// `Display` is similar to [`Debug`], but `Display` is for user-facing
/// output, and so cannot be derived.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
/// [tostring]: ../../std/string/trait.ToString.html
/// [tostring_function]: ../../std/string/trait.ToString.html#tymethod.to_string
///
/// # Examples
///
/// Implementing `Display` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// impl fmt::Display for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {})", self.x, self.y)
/// }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");
/// ```
#[rustc_on_unimplemented(
on(
any(_Self = "std::path::Path", _Self = "std::path::PathBuf"),
label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
as they may contain non-Unicode data"
),
message = "`{Self}` doesn't implement `{Display}`",
label = "`{Self}` cannot be formatted with the default formatter",
note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
)]
#[doc(alias = "{}")]
#[rustc_diagnostic_item = "Display"]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Display {
/// Formats the value using the given formatter.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Position {
/// longitude: f32,
/// latitude: f32,
/// }
///
/// impl fmt::Display for Position {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {})", self.longitude, self.latitude)
/// }
/// }
///
/// assert_eq!("(1.987, 2.983)",
/// format!("{}", Position { longitude: 1.987, latitude: 2.983, }));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `o` formatting.
///
/// The `Octal` trait should format its output as a number in base-8.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0o` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '52' in octal
///
/// assert_eq!(format!("{x:o}"), "52");
/// assert_eq!(format!("{x:#o}"), "0o52");
///
/// assert_eq!(format!("{:o}", -16), "37777777760");
/// ```
///
/// Implementing `Octal` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Octal for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::Octal::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(9);
///
/// assert_eq!(format!("l as octal is: {l:o}"), "l as octal is: 11");
///
/// assert_eq!(format!("l as octal is: {l:#06o}"), "l as octal is: 0o0011");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Octal {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `b` formatting.
///
/// The `Binary` trait should format its output as a number in binary.
///
/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0b` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with [`i32`]:
///
/// ```
/// let x = 42; // 42 is '101010' in binary
///
/// assert_eq!(format!("{x:b}"), "101010");
/// assert_eq!(format!("{x:#b}"), "0b101010");
///
/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
/// ```
///
/// Implementing `Binary` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Binary for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::Binary::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(107);
///
/// assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");
///
/// assert_eq!(
/// format!("l as binary is: {l:#032b}"),
/// "l as binary is: 0b000000000000000000000001101011"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Binary {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `x` formatting.
///
/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
/// in lower case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '2a' in hex
///
/// assert_eq!(format!("{x:x}"), "2a");
/// assert_eq!(format!("{x:#x}"), "0x2a");
///
/// assert_eq!(format!("{:x}", -16), "fffffff0");
/// ```
///
/// Implementing `LowerHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerHex for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(9);
///
/// assert_eq!(format!("l as hex is: {l:x}"), "l as hex is: 9");
///
/// assert_eq!(format!("l as hex is: {l:#010x}"), "l as hex is: 0x00000009");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerHex {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `X` formatting.
///
/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
/// in upper case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '2A' in hex
///
/// assert_eq!(format!("{x:X}"), "2A");
/// assert_eq!(format!("{x:#X}"), "0x2A");
///
/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
/// ```
///
/// Implementing `UpperHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperHex for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(i32::MAX);
///
/// assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");
///
/// assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperHex {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `p` formatting.
///
/// The `Pointer` trait should format its output as a memory location. This is commonly presented
/// as hexadecimal.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `&i32`:
///
/// ```
/// let x = &42;
///
/// let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'
/// ```
///
/// Implementing `Pointer` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Pointer for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// // use `as` to convert to a `*const T`, which implements Pointer, which we can use
///
/// let ptr = self as *const Self;
/// fmt::Pointer::fmt(&ptr, f)
/// }
/// }
///
/// let l = Length(42);
///
/// println!("l is in memory here: {l:p}");
///
/// let l_ptr = format!("{l:018p}");
/// assert_eq!(l_ptr.len(), 18);
/// assert_eq!(&l_ptr[..2], "0x");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Pointer"]
pub trait Pointer {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `e` formatting.
///
/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
///
/// assert_eq!(format!("{x:e}"), "4.2e1");
/// ```
///
/// Implementing `LowerExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerExp for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = f64::from(self.0);
/// fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
/// }
/// }
///
/// let l = Length(100);
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:e}"),
/// "l in scientific notation is: 1e2"
/// );
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:05e}"),
/// "l in scientific notation is: 001e2"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerExp {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `E` formatting.
///
/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
///
/// assert_eq!(format!("{x:E}"), "4.2E1");
/// ```
///
/// Implementing `UpperExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperExp for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = f64::from(self.0);
/// fmt::UpperExp::fmt(&val, f) // delegate to f64's implementation
/// }
/// }
///
/// let l = Length(100);
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:E}"),
/// "l in scientific notation is: 1E2"
/// );
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:05E}"),
/// "l in scientific notation is: 001E2"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperExp {
/// Formats the value using the given formatter.
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// The `write` function takes an output stream, and an `Arguments` struct
/// that can be precompiled with the `format_args!` macro.
///
/// The arguments will be formatted according to the specified format string
/// into the output stream provided.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::fmt;
///
/// let mut output = String::new();
/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
/// .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// Please note that using [`write!`] might be preferable. Example:
///
/// ```
/// use std::fmt::Write;
///
/// let mut output = String::new();
/// write!(&mut output, "Hello {}!", "world")
/// .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// [`write!`]: crate::write!
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
let mut formatter = Formatter::new(output);
let mut idx = 0;
match args.fmt {
None => {
// We can use default formatting parameters for all arguments.
for (i, arg) in args.args.iter().enumerate() {
// SAFETY: args.args and args.pieces come from the same Arguments,
// which guarantees the indexes are always within bounds.
let piece = unsafe { args.pieces.get_unchecked(i) };
if !piece.is_empty() {
formatter.buf.write_str(*piece)?;
}
(arg.formatter)(arg.value, &mut formatter)?;
idx += 1;
}
}
Some(fmt) => {
// Every spec has a corresponding argument that is preceded by
// a string piece.
for (i, arg) in fmt.iter().enumerate() {
// SAFETY: fmt and args.pieces come from the same Arguments,
// which guarantees the indexes are always within bounds.
let piece = unsafe { args.pieces.get_unchecked(i) };
if !piece.is_empty() {
formatter.buf.write_str(*piece)?;
}
// SAFETY: arg and args.args come from the same Arguments,
// which guarantees the indexes are always within bounds.
unsafe { run(&mut formatter, arg, args.args) }?;
idx += 1;
}
}
}
// There can be only one trailing string piece left.
if let Some(piece) = args.pieces.get(idx) {
formatter.buf.write_str(*piece)?;
}
Ok(())
}
unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::v1::Argument, args: &[ArgumentV1<'_>]) -> Result {
fmt.fill = arg.format.fill;
fmt.align = arg.format.align;
fmt.flags = arg.format.flags;
// SAFETY: arg and args come from the same Arguments,
// which guarantees the indexes are always within bounds.
unsafe {
fmt.width = getcount(args, &arg.format.width);
fmt.precision = getcount(args, &arg.format.precision);
}
// Extract the correct argument
debug_assert!(arg.position < args.len());
// SAFETY: arg and args come from the same Arguments,
// which guarantees its index is always within bounds.
let value = unsafe { args.get_unchecked(arg.position) };
// Then actually do some printing
(value.formatter)(value.value, fmt)
}
unsafe fn getcount(args: &[ArgumentV1<'_>], cnt: &rt::v1::Count) -> Option<usize> {
match *cnt {
rt::v1::Count::Is(n) => Some(n),
rt::v1::Count::Implied => None,
rt::v1::Count::Param(i) => {
debug_assert!(i < args.len());
// SAFETY: cnt and args come from the same Arguments,
// which guarantees this index is always within bounds.
unsafe { args.get_unchecked(i).as_usize() }
}
}
}
/// Padding after the end of something. Returned by `Formatter::padding`.
#[must_use = "don't forget to write the post padding"]
pub(crate) struct PostPadding {
fill: char,
padding: usize,
}
impl PostPadding {
fn new(fill: char, padding: usize) -> PostPadding {
PostPadding { fill, padding }
}
/// Write this post padding.
pub(crate) fn write(self, f: &mut Formatter<'_>) -> Result {
for _ in 0..self.padding {
f.buf.write_char(self.fill)?;
}
Ok(())
}
}
impl<'a> Formatter<'a> {
fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
where
'b: 'c,
F: FnOnce(&'b mut (dyn Write + 'b)) -> &'c mut (dyn Write + 'c),
{
Formatter {
// We want to change this
buf: wrap(self.buf),
// And preserve these
flags: self.flags,
fill: self.fill,
align: self.align,
width: self.width,
precision: self.precision,
}
}
// Helper methods used for padding and processing formatting arguments that
// all formatting traits can use.
/// Performs the correct padding for an integer which has already been
/// emitted into a str. The str should *not* contain the sign for the
/// integer, that will be added by this method.
///
/// # Arguments
///
/// * is_nonnegative - whether the original integer was either positive or zero.
/// * prefix - if the '#' character (Alternate) is provided, this
/// is the prefix to put in front of the number.
/// * buf - the byte array that the number has been formatted into
///
/// This function will correctly account for the flags provided as well as
/// the minimum width. It will not take precision into account.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo { nb: i32 }
///
/// impl Foo {
/// fn new(nb: i32) -> Foo {
/// Foo {
/// nb,
/// }
/// }
/// }
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// // We need to remove "-" from the number output.
/// let tmp = self.nb.abs().to_string();
///
/// formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
/// }
/// }
///
/// assert_eq!(&format!("{}", Foo::new(2)), "2");
/// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
/// assert_eq!(&format!("{}", Foo::new(0)), "0");
/// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
/// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
let mut width = buf.len();
let mut sign = None;
if !is_nonnegative {
sign = Some('-');
width += 1;
} else if self.sign_plus() {
sign = Some('+');
width += 1;
}
let prefix = if self.alternate() {
width += prefix.chars().count();
Some(prefix)
} else {
None
};
// Writes the sign if it exists, and then the prefix if it was requested
#[inline(never)]
fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
if let Some(c) = sign {
f.buf.write_char(c)?;
}
if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) }
}
// The `width` field is more of a `min-width` parameter at this point.
match self.width {
// If there's no minimum length requirements then we can just
// write the bytes.
None => {
write_prefix(self, sign, prefix)?;
self.buf.write_str(buf)
}
// Check if we're over the minimum width, if so then we can also
// just write the bytes.
Some(min) if width >= min => {
write_prefix(self, sign, prefix)?;
self.buf.write_str(buf)
}
// The sign and prefix goes before the padding if the fill character
// is zero
Some(min) if self.sign_aware_zero_pad() => {
let old_fill = crate::mem::replace(&mut self.fill, '0');
let old_align = crate::mem::replace(&mut self.align, rt::v1::Alignment::Right);
write_prefix(self, sign, prefix)?;
let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
self.buf.write_str(buf)?;
post_padding.write(self)?;
self.fill = old_fill;
self.align = old_align;
Ok(())
}
// Otherwise, the sign and prefix goes after the padding
Some(min) => {
let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
write_prefix(self, sign, prefix)?;
self.buf.write_str(buf)?;
post_padding.write(self)
}
}
}
/// This function takes a string slice and emits it to the internal buffer
/// after applying the relevant formatting flags specified. The flags
/// recognized for generic strings are:
///
/// * width - the minimum width of what to emit
/// * fill/align - what to emit and where to emit it if the string
/// provided needs to be padded
/// * precision - the maximum length to emit, the string is truncated if it
/// is longer than this length
///
/// Notably this function ignores the `flag` parameters.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// formatter.pad("Foo")
/// }
/// }
///
/// assert_eq!(&format!("{Foo:<4}"), "Foo ");
/// assert_eq!(&format!("{Foo:0>4}"), "0Foo");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pad(&mut self, s: &str) -> Result {
// Make sure there's a fast path up front
if self.width.is_none() && self.precision.is_none() {
return self.buf.write_str(s);
}
// The `precision` field can be interpreted as a `max-width` for the
// string being formatted.
let s = if let Some(max) = self.precision {
// If our string is longer that the precision, then we must have
// truncation. However other flags like `fill`, `width` and `align`
// must act as always.
if let Some((i, _)) = s.char_indices().nth(max) {
// LLVM here can't prove that `..i` won't panic `&s[..i]`, but
// we know that it can't panic. Use `get` + `unwrap_or` to avoid
// `unsafe` and otherwise don't emit any panic-related code
// here.
s.get(..i).unwrap_or(s)
} else {
&s
}
} else {
&s
};
// The `width` field is more of a `min-width` parameter at this point.
match self.width {
// If we're under the maximum length, and there's no minimum length
// requirements, then we can just emit the string
None => self.buf.write_str(s),
Some(width) => {
let chars_count = s.chars().count();
// If we're under the maximum width, check if we're over the minimum
// width, if so it's as easy as just emitting the string.
if chars_count >= width {
self.buf.write_str(s)
}
// If we're under both the maximum and the minimum width, then fill
// up the minimum width with the specified string + some alignment.
else {
let align = rt::v1::Alignment::Left;
let post_padding = self.padding(width - chars_count, align)?;
self.buf.write_str(s)?;
post_padding.write(self)
}
}
}
}
/// Write the pre-padding and return the unwritten post-padding. Callers are
/// responsible for ensuring post-padding is written after the thing that is
/// being padded.
pub(crate) fn padding(
&mut self,
padding: usize,
default: rt::v1::Alignment,
) -> result::Result<PostPadding, Error> {
let align = match self.align {
rt::v1::Alignment::Unknown => default,
_ => self.align,
};
let (pre_pad, post_pad) = match align {
rt::v1::Alignment::Left => (0, padding),
rt::v1::Alignment::Right | rt::v1::Alignment::Unknown => (padding, 0),
rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
};
for _ in 0..pre_pad {
self.buf.write_char(self.fill)?;
}
Ok(PostPadding::new(self.fill, post_pad))
}
/// Takes the formatted parts and applies the padding.
/// Assumes that the caller already has rendered the parts with required precision,
/// so that `self.precision` can be ignored.
fn pad_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
if let Some(mut width) = self.width {
// for the sign-aware zero padding, we render the sign first and
// behave as if we had no sign from the beginning.
let mut formatted = formatted.clone();
let old_fill = self.fill;
let old_align = self.align;
let mut align = old_align;
if self.sign_aware_zero_pad() {
// a sign always goes first
let sign = formatted.sign;
self.buf.write_str(sign)?;
// remove the sign from the formatted parts
formatted.sign = "";
width = width.saturating_sub(sign.len());
align = rt::v1::Alignment::Right;
self.fill = '0';
self.align = rt::v1::Alignment::Right;
}
// remaining parts go through the ordinary padding process.
let len = formatted.len();
let ret = if width <= len {
// no padding
self.write_formatted_parts(&formatted)
} else {
let post_padding = self.padding(width - len, align)?;
self.write_formatted_parts(&formatted)?;
post_padding.write(self)
};
self.fill = old_fill;
self.align = old_align;
ret
} else {
// this is the common case and we take a shortcut
self.write_formatted_parts(formatted)
}
}
fn write_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
// SAFETY: This is used for `numfmt::Part::Num` and `numfmt::Part::Copy`.
// It's safe to use for `numfmt::Part::Num` since every char `c` is between
// `b'0'` and `b'9'`, which means `s` is valid UTF-8.
// It's also probably safe in practice to use for `numfmt::Part::Copy(buf)`
// since `buf` should be plain ASCII, but it's possible for someone to pass
// in a bad value for `buf` into `numfmt::to_shortest_str` since it is a
// public function.
// FIXME: Determine whether this could result in UB.
buf.write_str(unsafe { str::from_utf8_unchecked(s) })
}
if !formatted.sign.is_empty() {
self.buf.write_str(formatted.sign)?;
}
for part in formatted.parts {
match *part {
numfmt::Part::Zero(mut nzeroes) => {
const ZEROES: &str = // 64 zeroes
"0000000000000000000000000000000000000000000000000000000000000000";
while nzeroes > ZEROES.len() {
self.buf.write_str(ZEROES)?;
nzeroes -= ZEROES.len();
}
if nzeroes > 0 {
self.buf.write_str(&ZEROES[..nzeroes])?;
}
}
numfmt::Part::Num(mut v) => {
let mut s = [0; 5];
let len = part.len();
for c in s[..len].iter_mut().rev() {
*c = b'0' + (v % 10) as u8;
v /= 10;
}
write_bytes(self.buf, &s[..len])?;
}
numfmt::Part::Copy(buf) => {
write_bytes(self.buf, buf)?;
}
}
}
Ok(())
}
/// Writes some data to the underlying buffer contained within this
/// formatter.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// formatter.write_str("Foo")
/// // This is equivalent to:
/// // write!(formatter, "Foo")
/// }
/// }
///
/// assert_eq!(&format!("{Foo}"), "Foo");
/// assert_eq!(&format!("{Foo:0>8}"), "Foo");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write_str(&mut self, data: &str) -> Result {
self.buf.write_str(data)
}
/// Writes some formatted information into this instance.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// formatter.write_fmt(format_args!("Foo {}", self.0))
/// }
/// }
///
/// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
/// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
write(self.buf, fmt)
}
/// Flags for formatting
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[deprecated(
since = "1.24.0",
note = "use the `sign_plus`, `sign_minus`, `alternate`, \
or `sign_aware_zero_pad` methods instead"
)]
pub fn flags(&self) -> u32 {
self.flags
}
/// Character used as 'fill' whenever there is alignment.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// let c = formatter.fill();
/// if let Some(width) = formatter.width() {
/// for _ in 0..width {
/// write!(formatter, "{c}")?;
/// }
/// Ok(())
/// } else {
/// write!(formatter, "{c}")
/// }
/// }
/// }
///
/// // We set alignment to the right with ">".
/// assert_eq!(&format!("{Foo:G>3}"), "GGG");
/// assert_eq!(&format!("{Foo:t>6}"), "tttttt");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn fill(&self) -> char {
self.fill
}
/// Flag indicating what form of alignment was requested.
///
/// # Examples
///
/// ```
/// extern crate core;
///
/// use std::fmt::{self, Alignment};
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// let s = if let Some(s) = formatter.align() {
/// match s {
/// Alignment::Left => "left",
/// Alignment::Right => "right",
/// Alignment::Center => "center",
/// }
/// } else {
/// "into the void"
/// };
/// write!(formatter, "{s}")
/// }
/// }
///
/// assert_eq!(&format!("{Foo:<}"), "left");
/// assert_eq!(&format!("{Foo:>}"), "right");
/// assert_eq!(&format!("{Foo:^}"), "center");
/// assert_eq!(&format!("{Foo}"), "into the void");
/// ```
#[must_use]
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
pub fn align(&self) -> Option<Alignment> {
match self.align {
rt::v1::Alignment::Left => Some(Alignment::Left),
rt::v1::Alignment::Right => Some(Alignment::Right),
rt::v1::Alignment::Center => Some(Alignment::Center),
rt::v1::Alignment::Unknown => None,
}
}
/// Optionally specified integer width that the output should be.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// if let Some(width) = formatter.width() {
/// // If we received a width, we use it
/// write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
/// } else {
/// // Otherwise we do nothing special
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23) ");
/// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn width(&self) -> Option<usize> {
self.width
}
/// Optionally specified precision for numeric types. Alternatively, the
/// maximum width for string types.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(f32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// if let Some(precision) = formatter.precision() {
/// // If we received a precision, we use it.
/// write!(formatter, "Foo({1:.*})", precision, self.0)
/// } else {
/// // Otherwise we default to 2.
/// write!(formatter, "Foo({:.2})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
/// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn precision(&self) -> Option<usize> {
self.precision
}
/// Determines if the `+` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// if formatter.sign_plus() {
/// write!(formatter,
/// "Foo({}{})",
/// if self.0 < 0 { '-' } else { '+' },
/// self.0.abs())
/// } else {
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
/// assert_eq!(&format!("{:+}", Foo(-23)), "Foo(-23)");
/// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_plus(&self) -> bool {
self.flags & (1 << FlagV1::SignPlus as u32) != 0
}
/// Determines if the `-` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// if formatter.sign_minus() {
/// // You want a minus sign? Have one!
/// write!(formatter, "-Foo({})", self.0)
/// } else {
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
/// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_minus(&self) -> bool {
self.flags & (1 << FlagV1::SignMinus as u32) != 0
}
/// Determines if the `#` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// if formatter.alternate() {
/// write!(formatter, "Foo({})", self.0)
/// } else {
/// write!(formatter, "{}", self.0)
/// }
/// }
/// }
///
/// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
/// assert_eq!(&format!("{}", Foo(23)), "23");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn alternate(&self) -> bool {
self.flags & (1 << FlagV1::Alternate as u32) != 0
}
/// Determines if the `0` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// assert!(formatter.sign_aware_zero_pad());
/// assert_eq!(formatter.width(), Some(4));
/// // We ignore the formatter's options.
/// write!(formatter, "{}", self.0)
/// }
/// }
///
/// assert_eq!(&format!("{:04}", Foo(23)), "23");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_aware_zero_pad(&self) -> bool {
self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
}
// FIXME: Decide what public API we want for these two flags.
// https://github.com/rust-lang/rust/issues/48584
fn debug_lower_hex(&self) -> bool {
self.flags & (1 << FlagV1::DebugLowerHex as u32) != 0
}
fn debug_upper_hex(&self) -> bool {
self.flags & (1 << FlagV1::DebugUpperHex as u32) != 0
}
/// Creates a [`DebugStruct`] builder designed to assist with creation of
/// [`fmt::Debug`] implementations for structs.
///
/// [`fmt::Debug`]: self::Debug
///
/// # Examples
///
/// ```rust
/// use std::fmt;
/// use std::net::Ipv4Addr;
///
/// struct Foo {
/// bar: i32,
/// baz: String,
/// addr: Ipv4Addr,
/// }
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_struct("Foo")
/// .field("bar", &self.bar)
/// .field("baz", &self.baz)
/// .field("addr", &format_args!("{}", self.addr))
/// .finish()
/// }
/// }
///
/// assert_eq!(
/// "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
/// format!("{:?}", Foo {
/// bar: 10,
/// baz: "Hello World".to_string(),
/// addr: Ipv4Addr::new(127, 0, 0, 1),
/// })
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
builders::debug_struct_new(self, name)
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_struct_fields_finish` is more general, but this is faster for 1 field.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field1_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_struct_fields_finish` is more general, but this is faster for 2 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field2_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_struct_fields_finish` is more general, but this is faster for 3 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field3_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_struct_fields_finish` is more general, but this is faster for 4 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field4_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
name4: &str,
value4: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.field(name4, value4);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_struct_fields_finish` is more general, but this is faster for 5 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field5_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
name4: &str,
value4: &dyn Debug,
name5: &str,
value5: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.field(name4, value4);
builder.field(name5, value5);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// For the cases not covered by `debug_struct_field[12345]_finish`.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_fields_finish<'b>(
&'b mut self,
name: &str,
names: &[&str],
values: &[&dyn Debug],
) -> Result {
assert_eq!(names.len(), values.len());
let mut builder = builders::debug_struct_new(self, name);
for (name, value) in iter::zip(names, values) {
builder.field(name, value);
}
builder.finish()
}
/// Creates a `DebugTuple` builder designed to assist with creation of
/// `fmt::Debug` implementations for tuple structs.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
/// use std::marker::PhantomData;
///
/// struct Foo<T>(i32, String, PhantomData<T>);
///
/// impl<T> fmt::Debug for Foo<T> {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_tuple("Foo")
/// .field(&self.0)
/// .field(&self.1)
/// .field(&format_args!("_"))
/// .finish()
/// }
/// }
///
/// assert_eq!(
/// "Foo(10, \"Hello\", _)",
/// format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
builders::debug_tuple_new(self, name)
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_tuple_fields_finish` is more general, but this is faster for 1 field.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field1_finish<'b>(&'b mut self, name: &str, value1: &dyn Debug) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_tuple_fields_finish` is more general, but this is faster for 2 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field2_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_tuple_fields_finish` is more general, but this is faster for 3 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field3_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_tuple_fields_finish` is more general, but this is faster for 4 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field4_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
value4: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.field(value4);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// `debug_tuple_fields_finish` is more general, but this is faster for 5 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field5_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
value4: &dyn Debug,
value5: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.field(value4);
builder.field(value5);
builder.finish()
}
/// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
/// For the cases not covered by `debug_tuple_field[12345]_finish`.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_fields_finish<'b>(
&'b mut self,
name: &str,
values: &[&dyn Debug],
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
for value in values {
builder.field(value);
}
builder.finish()
}
/// Creates a `DebugList` builder designed to assist with creation of
/// `fmt::Debug` implementations for list-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<i32>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_list().entries(self.0.iter()).finish()
/// }
/// }
///
/// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
builders::debug_list_new(self)
}
/// Creates a `DebugSet` builder designed to assist with creation of
/// `fmt::Debug` implementations for set-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<i32>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_set().entries(self.0.iter()).finish()
/// }
/// }
///
/// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");
/// ```
///
/// [`format_args!`]: crate::format_args
///
/// In this more complex example, we use [`format_args!`] and `.debug_set()`
/// to build a list of match arms:
///
/// ```rust
/// use std::fmt;
///
/// struct Arm<'a, L: 'a, R: 'a>(&'a (L, R));
/// struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V);
///
/// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
/// where
/// L: 'a + fmt::Debug, R: 'a + fmt::Debug
/// {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// L::fmt(&(self.0).0, fmt)?;
/// fmt.write_str(" => ")?;
/// R::fmt(&(self.0).1, fmt)
/// }
/// }
///
/// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
/// where
/// K: 'a + fmt::Debug, V: 'a + fmt::Debug
/// {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_set()
/// .entries(self.0.iter().map(Arm))
/// .entry(&Arm(&(format_args!("_"), &self.1)))
/// .finish()
/// }
/// }
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
builders::debug_set_new(self)
}
/// Creates a `DebugMap` builder designed to assist with creation of
/// `fmt::Debug` implementations for map-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<(String, i32)>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
/// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
/// }
/// }
///
/// assert_eq!(
/// format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
/// r#"{"A": 10, "B": 11}"#
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
builders::debug_map_new(self)
}
}
#[stable(since = "1.2.0", feature = "formatter_write")]
impl Write for Formatter<'_> {
fn write_str(&mut self, s: &str) -> Result {
self.buf.write_str(s)
}
fn write_char(&mut self, c: char) -> Result {
self.buf.write_char(c)
}
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
write(self.buf, args)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Error {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt("an error occurred when formatting an argument", f)
}
}
// Implementations of the core formatting traits
macro_rules! fmt_refs {
($($tr:ident),*) => {
$(
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + $tr> $tr for &T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + $tr> $tr for &mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
}
)*
}
}
fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
#[unstable(feature = "never_type", issue = "35121")]
impl Debug for ! {
fn fmt(&self, _: &mut Formatter<'_>) -> Result {
*self
}
}
#[unstable(feature = "never_type", issue = "35121")]
impl Display for ! {
fn fmt(&self, _: &mut Formatter<'_>) -> Result {
*self
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for bool {
#[inline]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt(self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for bool {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt(if *self { "true" } else { "false" }, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for str {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.write_char('"')?;
let mut from = 0;
for (i, c) in self.char_indices() {
let esc = c.escape_debug_ext(EscapeDebugExtArgs {
escape_grapheme_extended: true,
escape_single_quote: false,
escape_double_quote: true,
});
// If char needs escaping, flush backlog so far and write, else skip
if esc.len() != 1 {
f.write_str(&self[from..i])?;
for c in esc {
f.write_char(c)?;
}
from = i + c.len_utf8();
}
}
f.write_str(&self[from..])?;
f.write_char('"')
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for str {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.pad(self)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for char {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.write_char('\'')?;
for c in self.escape_debug_ext(EscapeDebugExtArgs {
escape_grapheme_extended: true,
escape_single_quote: true,
escape_double_quote: false,
}) {
f.write_char(c)?
}
f.write_char('\'')
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for char {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
if f.width.is_none() && f.precision.is_none() {
f.write_char(*self)
} else {
f.pad(self.encode_utf8(&mut [0; 4]))
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *const T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
// Cast is needed here because `.addr()` requires `T: Sized`.
pointer_fmt_inner((*self as *const ()).addr(), f)
}
}
/// Since the formatting will be identical for all pointer types, use a non-monomorphized
/// implementation for the actual formatting to reduce the amount of codegen work needed.
///
/// This uses `ptr_addr: usize` and not `ptr: *const ()` to be able to use this for
/// `fn(...) -> ...` without using [problematic] "Oxford Casts".
///
/// [problematic]: https://github.com/rust-lang/rust/issues/95489
pub(crate) fn pointer_fmt_inner(ptr_addr: usize, f: &mut Formatter<'_>) -> Result {
let old_width = f.width;
let old_flags = f.flags;
// The alternate flag is already treated by LowerHex as being special-
// it denotes whether to prefix with 0x. We use it to work out whether
// or not to zero extend, and then unconditionally set it to get the
// prefix.
if f.alternate() {
f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
if f.width.is_none() {
f.width = Some((usize::BITS / 4) as usize + 2);
}
}
f.flags |= 1 << (FlagV1::Alternate as u32);
let ret = LowerHex::fmt(&ptr_addr, f);
f.width = old_width;
f.flags = old_flags;
ret
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(*self as *const T), f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(*self as *const T), f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(&**self as *const T), f)
}
}
// Implementation of Display/Debug for various core types
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *const T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(self, f)
}
}
macro_rules! peel {
($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
}
macro_rules! tuple {
() => ();
( $($name:ident,)+ ) => (
maybe_tuple_doc! {
$($name)+ @
#[stable(feature = "rust1", since = "1.0.0")]
impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
#[allow(non_snake_case, unused_assignments)]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
let mut builder = f.debug_tuple("");
let ($(ref $name,)+) = *self;
$(
builder.field(&$name);
)+
builder.finish()
}
}
}
peel! { $($name,)+ }
)
}
macro_rules! maybe_tuple_doc {
($a:ident @ #[$meta:meta] $item:item) => {
#[doc(fake_variadic)]
#[doc = "This trait is implemented for tuples up to twelve items long."]
#[$meta]
$item
};
($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
#[doc(hidden)]
#[$meta]
$item
};
}
macro_rules! last_type {
($a:ident,) => { $a };
($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
}
tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Debug> Debug for [T] {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_list().entries(self.iter()).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for () {
#[inline]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.pad("()")
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for PhantomData<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Copy + Debug> Debug for Cell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("Cell").field("value", &self.get()).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
match self.try_borrow() {
Ok(borrow) => f.debug_struct("RefCell").field("value", &borrow).finish(),
Err(_) => {
// The RefCell is mutably borrowed so we can't look at its value
// here. Show a placeholder instead.
struct BorrowedPlaceholder;
impl Debug for BorrowedPlaceholder {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.write_str("<borrowed>")
}
}
f.debug_struct("RefCell").field("value", &BorrowedPlaceholder).finish()
}
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Debug::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Debug::fmt(&*(self.deref()), f)
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T: ?Sized> Debug for UnsafeCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("UnsafeCell").finish_non_exhaustive()
}
}
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
impl<T: ?Sized> Debug for SyncUnsafeCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("SyncUnsafeCell").finish_non_exhaustive()
}
}
// If you expected tests to be here, look instead at the core/tests/fmt.rs file,
// it's a lot easier than creating all of the rt::Piece structures here.
// There are also tests in the alloc crate, for those that need allocations.