| //! Utilities for dynamic typing or type reflection. |
| //! |
| //! # `Any` and `TypeId` |
| //! |
| //! `Any` itself can be used to get a `TypeId`, and has more features when used |
| //! as a trait object. As `&dyn Any` (a borrowed trait object), it has the `is` |
| //! and `downcast_ref` methods, to test if the contained value is of a given type, |
| //! and to get a reference to the inner value as a type. As `&mut dyn Any`, there |
| //! is also the `downcast_mut` method, for getting a mutable reference to the |
| //! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to |
| //! convert to a `Box<T>`. See the [`Box`] documentation for the full details. |
| //! |
| //! Note that `&dyn Any` is limited to testing whether a value is of a specified |
| //! concrete type, and cannot be used to test whether a type implements a trait. |
| //! |
| //! [`Box`]: ../../std/boxed/struct.Box.html |
| //! |
| //! # Smart pointers and `dyn Any` |
| //! |
| //! One piece of behavior to keep in mind when using `Any` as a trait object, |
| //! especially with types like `Box<dyn Any>` or `Arc<dyn Any>`, is that simply |
| //! calling `.type_id()` on the value will produce the `TypeId` of the |
| //! *container*, not the underlying trait object. This can be avoided by |
| //! converting the smart pointer into a `&dyn Any` instead, which will return |
| //! the object's `TypeId`. For example: |
| //! |
| //! ``` |
| //! use std::any::{Any, TypeId}; |
| //! |
| //! let boxed: Box<dyn Any> = Box::new(3_i32); |
| //! |
| //! // You're more likely to want this: |
| //! let actual_id = (&*boxed).type_id(); |
| //! // ... than this: |
| //! let boxed_id = boxed.type_id(); |
| //! |
| //! assert_eq!(actual_id, TypeId::of::<i32>()); |
| //! assert_eq!(boxed_id, TypeId::of::<Box<dyn Any>>()); |
| //! ``` |
| //! |
| //! ## Examples |
| //! |
| //! Consider a situation where we want to log out a value passed to a function. |
| //! We know the value we're working on implements Debug, but we don't know its |
| //! concrete type. We want to give special treatment to certain types: in this |
| //! case printing out the length of String values prior to their value. |
| //! We don't know the concrete type of our value at compile time, so we need to |
| //! use runtime reflection instead. |
| //! |
| //! ```rust |
| //! use std::fmt::Debug; |
| //! use std::any::Any; |
| //! |
| //! // Logger function for any type that implements Debug. |
| //! fn log<T: Any + Debug>(value: &T) { |
| //! let value_any = value as &dyn Any; |
| //! |
| //! // Try to convert our value to a `String`. If successful, we want to |
| //! // output the String`'s length as well as its value. If not, it's a |
| //! // different type: just print it out unadorned. |
| //! match value_any.downcast_ref::<String>() { |
| //! Some(as_string) => { |
| //! println!("String ({}): {}", as_string.len(), as_string); |
| //! } |
| //! None => { |
| //! println!("{value:?}"); |
| //! } |
| //! } |
| //! } |
| //! |
| //! // This function wants to log its parameter out prior to doing work with it. |
| //! fn do_work<T: Any + Debug>(value: &T) { |
| //! log(value); |
| //! // ...do some other work |
| //! } |
| //! |
| //! fn main() { |
| //! let my_string = "Hello World".to_string(); |
| //! do_work(&my_string); |
| //! |
| //! let my_i8: i8 = 100; |
| //! do_work(&my_i8); |
| //! } |
| //! ``` |
| //! |
| //! # `Provider` and `Demand` |
| //! |
| //! `Provider` and the associated APIs support generic, type-driven access to data, and a mechanism |
| //! for implementers to provide such data. The key parts of the interface are the `Provider` |
| //! trait for objects which can provide data, and the [`request_value`] and [`request_ref`] |
| //! functions for requesting data from an object which implements `Provider`. Generally, end users |
| //! should not call `request_*` directly, they are helper functions for intermediate implementers |
| //! to use to implement a user-facing interface. This is purely for the sake of ergonomics, there is |
| //! no safety concern here; intermediate implementers can typically support methods rather than |
| //! free functions and use more specific names. |
| //! |
| //! Typically, a data provider is a trait object of a trait which extends `Provider`. A user will |
| //! request data from a trait object by specifying the type of the data. |
| //! |
| //! ## Data flow |
| //! |
| //! * A user requests an object of a specific type, which is delegated to `request_value` or |
| //! `request_ref` |
| //! * `request_*` creates a `Demand` object and passes it to `Provider::provide` |
| //! * The data provider's implementation of `Provider::provide` tries providing values of |
| //! different types using `Demand::provide_*`. If the type matches the type requested by |
| //! the user, the value will be stored in the `Demand` object. |
| //! * `request_*` unpacks the `Demand` object and returns any stored value to the user. |
| //! |
| //! ## Examples |
| //! |
| //! ``` |
| //! # #![feature(provide_any)] |
| //! use std::any::{Provider, Demand, request_ref}; |
| //! |
| //! // Definition of MyTrait, a data provider. |
| //! trait MyTrait: Provider { |
| //! // ... |
| //! } |
| //! |
| //! // Methods on `MyTrait` trait objects. |
| //! impl dyn MyTrait + '_ { |
| //! /// Get a reference to a field of the implementing struct. |
| //! pub fn get_context_by_ref<T: ?Sized + 'static>(&self) -> Option<&T> { |
| //! request_ref::<T>(self) |
| //! } |
| //! } |
| //! |
| //! // Downstream implementation of `MyTrait` and `Provider`. |
| //! # struct SomeConcreteType { some_string: String } |
| //! impl MyTrait for SomeConcreteType { |
| //! // ... |
| //! } |
| //! |
| //! impl Provider for SomeConcreteType { |
| //! fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| //! // Provide a string reference. We could provide multiple values with |
| //! // different types here. |
| //! demand.provide_ref::<String>(&self.some_string); |
| //! } |
| //! } |
| //! |
| //! // Downstream usage of `MyTrait`. |
| //! fn use_my_trait(obj: &dyn MyTrait) { |
| //! // Request a &String from obj. |
| //! let _ = obj.get_context_by_ref::<String>().unwrap(); |
| //! } |
| //! ``` |
| //! |
| //! In this example, if the concrete type of `obj` in `use_my_trait` is `SomeConcreteType`, then |
| //! the `get_context_ref` call will return a reference to `obj.some_string` with type `&String`. |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use crate::fmt; |
| use crate::intrinsics; |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Any trait |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// A trait to emulate dynamic typing. |
| /// |
| /// Most types implement `Any`. However, any type which contains a non-`'static` reference does not. |
| /// See the [module-level documentation][mod] for more details. |
| /// |
| /// [mod]: crate::any |
| // This trait is not unsafe, though we rely on the specifics of it's sole impl's |
| // `type_id` function in unsafe code (e.g., `downcast`). Normally, that would be |
| // a problem, but because the only impl of `Any` is a blanket implementation, no |
| // other code can implement `Any`. |
| // |
| // We could plausibly make this trait unsafe -- it would not cause breakage, |
| // since we control all the implementations -- but we choose not to as that's |
| // both not really necessary and may confuse users about the distinction of |
| // unsafe traits and unsafe methods (i.e., `type_id` would still be safe to call, |
| // but we would likely want to indicate as such in documentation). |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[cfg_attr(not(test), rustc_diagnostic_item = "Any")] |
| pub trait Any: 'static { |
| /// Gets the `TypeId` of `self`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::{Any, TypeId}; |
| /// |
| /// fn is_string(s: &dyn Any) -> bool { |
| /// TypeId::of::<String>() == s.type_id() |
| /// } |
| /// |
| /// assert_eq!(is_string(&0), false); |
| /// assert_eq!(is_string(&"cookie monster".to_string()), true); |
| /// ``` |
| #[stable(feature = "get_type_id", since = "1.34.0")] |
| fn type_id(&self) -> TypeId; |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: 'static + ?Sized> Any for T { |
| fn type_id(&self) -> TypeId { |
| TypeId::of::<T>() |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Extension methods for Any trait objects. |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl fmt::Debug for dyn Any { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| // Ensure that the result of e.g., joining a thread can be printed and |
| // hence used with `unwrap`. May eventually no longer be needed if |
| // dispatch works with upcasting. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl fmt::Debug for dyn Any + Send { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| impl fmt::Debug for dyn Any + Send + Sync { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| impl dyn Any { |
| /// Returns `true` if the inner type is the same as `T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &dyn Any) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| // Get `TypeId` of the type this function is instantiated with. |
| let t = TypeId::of::<T>(); |
| |
| // Get `TypeId` of the type in the trait object (`self`). |
| let concrete = self.type_id(); |
| |
| // Compare both `TypeId`s on equality. |
| t == concrete |
| } |
| |
| /// Returns some reference to the inner value if it is of type `T`, or |
| /// `None` if it isn't. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &dyn Any) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| if self.is::<T>() { |
| // SAFETY: just checked whether we are pointing to the correct type, and we can rely on |
| // that check for memory safety because we have implemented Any for all types; no other |
| // impls can exist as they would conflict with our impl. |
| unsafe { Some(self.downcast_ref_unchecked()) } |
| } else { |
| None |
| } |
| } |
| |
| /// Returns some mutable reference to the inner value if it is of type `T`, or |
| /// `None` if it isn't. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut dyn Any) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| if self.is::<T>() { |
| // SAFETY: just checked whether we are pointing to the correct type, and we can rely on |
| // that check for memory safety because we have implemented Any for all types; no other |
| // impls can exist as they would conflict with our impl. |
| unsafe { Some(self.downcast_mut_unchecked()) } |
| } else { |
| None |
| } |
| } |
| |
| /// Returns a reference to the inner value as type `dyn T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// The contained value must be of type `T`. Calling this method |
| /// with the incorrect type is *undefined behavior*. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| debug_assert!(self.is::<T>()); |
| // SAFETY: caller guarantees that T is the correct type |
| unsafe { &*(self as *const dyn Any as *const T) } |
| } |
| |
| /// Returns a mutable reference to the inner value as type `dyn T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// The contained value must be of type `T`. Calling this method |
| /// with the incorrect type is *undefined behavior*. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| debug_assert!(self.is::<T>()); |
| // SAFETY: caller guarantees that T is the correct type |
| unsafe { &mut *(self as *mut dyn Any as *mut T) } |
| } |
| } |
| |
| impl dyn Any + Send { |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &(dyn Any + Send)) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| <dyn Any>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &(dyn Any + Send)) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| <dyn Any>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut (dyn Any + Send)) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| <dyn Any>::downcast_mut::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// Same as the method on the type `dyn Any`. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) } |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// Same as the method on the type `dyn Any`. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_mut_unchecked::<T>(self) } |
| } |
| } |
| |
| impl dyn Any + Send + Sync { |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &(dyn Any + Send + Sync)) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| <dyn Any>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &(dyn Any + Send + Sync)) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| <dyn Any>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut (dyn Any + Send + Sync)) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| <dyn Any>::downcast_mut::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) } |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_mut_unchecked::<T>(self) } |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // TypeID and its methods |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// A `TypeId` represents a globally unique identifier for a type. |
| /// |
| /// Each `TypeId` is an opaque object which does not allow inspection of what's |
| /// inside but does allow basic operations such as cloning, comparison, |
| /// printing, and showing. |
| /// |
| /// A `TypeId` is currently only available for types which ascribe to `'static`, |
| /// but this limitation may be removed in the future. |
| /// |
| /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth |
| /// noting that the hashes and ordering will vary between Rust releases. Beware |
| /// of relying on them inside of your code! |
| #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct TypeId { |
| t: u64, |
| } |
| |
| impl TypeId { |
| /// Returns the `TypeId` of the type this generic function has been |
| /// instantiated with. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::{Any, TypeId}; |
| /// |
| /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool { |
| /// TypeId::of::<String>() == TypeId::of::<T>() |
| /// } |
| /// |
| /// assert_eq!(is_string(&0), false); |
| /// assert_eq!(is_string(&"cookie monster".to_string()), true); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_unstable(feature = "const_type_id", issue = "77125")] |
| pub const fn of<T: ?Sized + 'static>() -> TypeId { |
| TypeId { t: intrinsics::type_id::<T>() } |
| } |
| } |
| |
| /// Returns the name of a type as a string slice. |
| /// |
| /// # Note |
| /// |
| /// This is intended for diagnostic use. The exact contents and format of the |
| /// string returned are not specified, other than being a best-effort |
| /// description of the type. For example, amongst the strings |
| /// that `type_name::<Option<String>>()` might return are `"Option<String>"` and |
| /// `"std::option::Option<std::string::String>"`. |
| /// |
| /// The returned string must not be considered to be a unique identifier of a |
| /// type as multiple types may map to the same type name. Similarly, there is no |
| /// guarantee that all parts of a type will appear in the returned string: for |
| /// example, lifetime specifiers are currently not included. In addition, the |
| /// output may change between versions of the compiler. |
| /// |
| /// The current implementation uses the same infrastructure as compiler |
| /// diagnostics and debuginfo, but this is not guaranteed. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// assert_eq!( |
| /// std::any::type_name::<Option<String>>(), |
| /// "core::option::Option<alloc::string::String>", |
| /// ); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "type_name", since = "1.38.0")] |
| #[rustc_const_unstable(feature = "const_type_name", issue = "63084")] |
| pub const fn type_name<T: ?Sized>() -> &'static str { |
| intrinsics::type_name::<T>() |
| } |
| |
| /// Returns the name of the type of the pointed-to value as a string slice. |
| /// This is the same as `type_name::<T>()`, but can be used where the type of a |
| /// variable is not easily available. |
| /// |
| /// # Note |
| /// |
| /// This is intended for diagnostic use. The exact contents and format of the |
| /// string are not specified, other than being a best-effort description of the |
| /// type. For example, `type_name_of_val::<Option<String>>(None)` could return |
| /// `"Option<String>"` or `"std::option::Option<std::string::String>"`, but not |
| /// `"foobar"`. In addition, the output may change between versions of the |
| /// compiler. |
| /// |
| /// This function does not resolve trait objects, |
| /// meaning that `type_name_of_val(&7u32 as &dyn Debug)` |
| /// may return `"dyn Debug"`, but not `"u32"`. |
| /// |
| /// The type name should not be considered a unique identifier of a type; |
| /// multiple types may share the same type name. |
| /// |
| /// The current implementation uses the same infrastructure as compiler |
| /// diagnostics and debuginfo, but this is not guaranteed. |
| /// |
| /// # Examples |
| /// |
| /// Prints the default integer and float types. |
| /// |
| /// ```rust |
| /// #![feature(type_name_of_val)] |
| /// use std::any::type_name_of_val; |
| /// |
| /// let x = 1; |
| /// println!("{}", type_name_of_val(&x)); |
| /// let y = 1.0; |
| /// println!("{}", type_name_of_val(&y)); |
| /// ``` |
| #[must_use] |
| #[unstable(feature = "type_name_of_val", issue = "66359")] |
| #[rustc_const_unstable(feature = "const_type_name", issue = "63084")] |
| pub const fn type_name_of_val<T: ?Sized>(_val: &T) -> &'static str { |
| type_name::<T>() |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Provider trait |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// Trait implemented by a type which can dynamically provide values based on type. |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub trait Provider { |
| /// Data providers should implement this method to provide *all* values they are able to |
| /// provide by using `demand`. |
| /// |
| /// Note that the `provide_*` methods on `Demand` have short-circuit semantics: if an earlier |
| /// method has successfully provided a value, then later methods will not get an opportunity to |
| /// provide. |
| /// |
| /// # Examples |
| /// |
| /// Provides a reference to a field with type `String` as a `&str`, and a value of |
| /// type `i32`. |
| /// |
| /// ```rust |
| /// # #![feature(provide_any)] |
| /// use std::any::{Provider, Demand}; |
| /// # struct SomeConcreteType { field: String, num_field: i32 } |
| /// |
| /// impl Provider for SomeConcreteType { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// demand.provide_ref::<str>(&self.field) |
| /// .provide_value::<i32>(self.num_field); |
| /// } |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| fn provide<'a>(&'a self, demand: &mut Demand<'a>); |
| } |
| |
| /// Request a value from the `Provider`. |
| /// |
| /// # Examples |
| /// |
| /// Get a string value from a provider. |
| /// |
| /// ```rust |
| /// # #![feature(provide_any)] |
| /// use std::any::{Provider, request_value}; |
| /// |
| /// fn get_string(provider: &impl Provider) -> String { |
| /// request_value::<String>(provider).unwrap() |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn request_value<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<T> |
| where |
| T: 'static, |
| { |
| request_by_type_tag::<'a, tags::Value<T>>(provider) |
| } |
| |
| /// Request a reference from the `Provider`. |
| /// |
| /// # Examples |
| /// |
| /// Get a string reference from a provider. |
| /// |
| /// ```rust |
| /// # #![feature(provide_any)] |
| /// use std::any::{Provider, request_ref}; |
| /// |
| /// fn get_str(provider: &impl Provider) -> &str { |
| /// request_ref::<str>(provider).unwrap() |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn request_ref<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<&'a T> |
| where |
| T: 'static + ?Sized, |
| { |
| request_by_type_tag::<'a, tags::Ref<tags::MaybeSizedValue<T>>>(provider) |
| } |
| |
| /// Request a specific value by tag from the `Provider`. |
| fn request_by_type_tag<'a, I>(provider: &'a (impl Provider + ?Sized)) -> Option<I::Reified> |
| where |
| I: tags::Type<'a>, |
| { |
| let mut tagged = TaggedOption::<'a, I>(None); |
| provider.provide(tagged.as_demand()); |
| tagged.0 |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Demand and its methods |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// A helper object for providing data by type. |
| /// |
| /// A data provider provides values by calling this type's provide methods. |
| #[unstable(feature = "provide_any", issue = "96024")] |
| #[repr(transparent)] |
| pub struct Demand<'a>(dyn Erased<'a> + 'a); |
| |
| impl<'a> Demand<'a> { |
| /// Create a new `&mut Demand` from a `&mut dyn Erased` trait object. |
| fn new<'b>(erased: &'b mut (dyn Erased<'a> + 'a)) -> &'b mut Demand<'a> { |
| // SAFETY: transmuting `&mut (dyn Erased<'a> + 'a)` to `&mut Demand<'a>` is safe since |
| // `Demand` is repr(transparent). |
| unsafe { &mut *(erased as *mut dyn Erased<'a> as *mut Demand<'a>) } |
| } |
| |
| /// Provide a value or other type with only static lifetimes. |
| /// |
| /// # Examples |
| /// |
| /// Provides an `u8`. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// # struct SomeConcreteType { field: u8 } |
| /// |
| /// impl Provider for SomeConcreteType { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// demand.provide_value::<u8>(self.field); |
| /// } |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn provide_value<T>(&mut self, value: T) -> &mut Self |
| where |
| T: 'static, |
| { |
| self.provide::<tags::Value<T>>(value) |
| } |
| |
| /// Provide a value or other type with only static lifetimes computed using a closure. |
| /// |
| /// # Examples |
| /// |
| /// Provides a `String` by cloning. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// # struct SomeConcreteType { field: String } |
| /// |
| /// impl Provider for SomeConcreteType { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// demand.provide_value_with::<String>(|| self.field.clone()); |
| /// } |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn provide_value_with<T>(&mut self, fulfil: impl FnOnce() -> T) -> &mut Self |
| where |
| T: 'static, |
| { |
| self.provide_with::<tags::Value<T>>(fulfil) |
| } |
| |
| /// Provide a reference. The referee type must be bounded by `'static`, |
| /// but may be unsized. |
| /// |
| /// # Examples |
| /// |
| /// Provides a reference to a field as a `&str`. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// # struct SomeConcreteType { field: String } |
| /// |
| /// impl Provider for SomeConcreteType { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// demand.provide_ref::<str>(&self.field); |
| /// } |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn provide_ref<T: ?Sized + 'static>(&mut self, value: &'a T) -> &mut Self { |
| self.provide::<tags::Ref<tags::MaybeSizedValue<T>>>(value) |
| } |
| |
| /// Provide a reference computed using a closure. The referee type |
| /// must be bounded by `'static`, but may be unsized. |
| /// |
| /// # Examples |
| /// |
| /// Provides a reference to a field as a `&str`. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// # struct SomeConcreteType { business: String, party: String } |
| /// # fn today_is_a_weekday() -> bool { true } |
| /// |
| /// impl Provider for SomeConcreteType { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// demand.provide_ref_with::<str>(|| { |
| /// if today_is_a_weekday() { |
| /// &self.business |
| /// } else { |
| /// &self.party |
| /// } |
| /// }); |
| /// } |
| /// } |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn provide_ref_with<T: ?Sized + 'static>( |
| &mut self, |
| fulfil: impl FnOnce() -> &'a T, |
| ) -> &mut Self { |
| self.provide_with::<tags::Ref<tags::MaybeSizedValue<T>>>(fulfil) |
| } |
| |
| /// Provide a value with the given `Type` tag. |
| fn provide<I>(&mut self, value: I::Reified) -> &mut Self |
| where |
| I: tags::Type<'a>, |
| { |
| if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() { |
| res.0 = Some(value); |
| } |
| self |
| } |
| |
| /// Provide a value with the given `Type` tag, using a closure to prevent unnecessary work. |
| fn provide_with<I>(&mut self, fulfil: impl FnOnce() -> I::Reified) -> &mut Self |
| where |
| I: tags::Type<'a>, |
| { |
| if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() { |
| res.0 = Some(fulfil()); |
| } |
| self |
| } |
| |
| /// Check if the `Demand` would be satisfied if provided with a |
| /// value of the specified type. If the type does not match or has |
| /// already been provided, returns false. |
| /// |
| /// # Examples |
| /// |
| /// Check if an `u8` still needs to be provided and then provides |
| /// it. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// |
| /// struct Parent(Option<u8>); |
| /// |
| /// impl Provider for Parent { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// if let Some(v) = self.0 { |
| /// demand.provide_value::<u8>(v); |
| /// } |
| /// } |
| /// } |
| /// |
| /// struct Child { |
| /// parent: Parent, |
| /// } |
| /// |
| /// impl Child { |
| /// // Pretend that this takes a lot of resources to evaluate. |
| /// fn an_expensive_computation(&self) -> Option<u8> { |
| /// Some(99) |
| /// } |
| /// } |
| /// |
| /// impl Provider for Child { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// // In general, we don't know if this call will provide |
| /// // an `u8` value or not... |
| /// self.parent.provide(demand); |
| /// |
| /// // ...so we check to see if the `u8` is needed before |
| /// // we run our expensive computation. |
| /// if demand.would_be_satisfied_by_value_of::<u8>() { |
| /// if let Some(v) = self.an_expensive_computation() { |
| /// demand.provide_value::<u8>(v); |
| /// } |
| /// } |
| /// |
| /// // The demand will be satisfied now, regardless of if |
| /// // the parent provided the value or we did. |
| /// assert!(!demand.would_be_satisfied_by_value_of::<u8>()); |
| /// } |
| /// } |
| /// |
| /// let parent = Parent(Some(42)); |
| /// let child = Child { parent }; |
| /// assert_eq!(Some(42), std::any::request_value::<u8>(&child)); |
| /// |
| /// let parent = Parent(None); |
| /// let child = Child { parent }; |
| /// assert_eq!(Some(99), std::any::request_value::<u8>(&child)); |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn would_be_satisfied_by_value_of<T>(&self) -> bool |
| where |
| T: 'static, |
| { |
| self.would_be_satisfied_by::<tags::Value<T>>() |
| } |
| |
| /// Check if the `Demand` would be satisfied if provided with a |
| /// reference to a value of the specified type. If the type does |
| /// not match or has already been provided, returns false. |
| /// |
| /// # Examples |
| /// |
| /// Check if a `&str` still needs to be provided and then provides |
| /// it. |
| /// |
| /// ```rust |
| /// #![feature(provide_any)] |
| /// |
| /// use std::any::{Provider, Demand}; |
| /// |
| /// struct Parent(Option<String>); |
| /// |
| /// impl Provider for Parent { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// if let Some(v) = &self.0 { |
| /// demand.provide_ref::<str>(v); |
| /// } |
| /// } |
| /// } |
| /// |
| /// struct Child { |
| /// parent: Parent, |
| /// name: String, |
| /// } |
| /// |
| /// impl Child { |
| /// // Pretend that this takes a lot of resources to evaluate. |
| /// fn an_expensive_computation(&self) -> Option<&str> { |
| /// Some(&self.name) |
| /// } |
| /// } |
| /// |
| /// impl Provider for Child { |
| /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { |
| /// // In general, we don't know if this call will provide |
| /// // a `str` reference or not... |
| /// self.parent.provide(demand); |
| /// |
| /// // ...so we check to see if the `&str` is needed before |
| /// // we run our expensive computation. |
| /// if demand.would_be_satisfied_by_ref_of::<str>() { |
| /// if let Some(v) = self.an_expensive_computation() { |
| /// demand.provide_ref::<str>(v); |
| /// } |
| /// } |
| /// |
| /// // The demand will be satisfied now, regardless of if |
| /// // the parent provided the reference or we did. |
| /// assert!(!demand.would_be_satisfied_by_ref_of::<str>()); |
| /// } |
| /// } |
| /// |
| /// let parent = Parent(Some("parent".into())); |
| /// let child = Child { parent, name: "child".into() }; |
| /// assert_eq!(Some("parent"), std::any::request_ref::<str>(&child)); |
| /// |
| /// let parent = Parent(None); |
| /// let child = Child { parent, name: "child".into() }; |
| /// assert_eq!(Some("child"), std::any::request_ref::<str>(&child)); |
| /// ``` |
| #[unstable(feature = "provide_any", issue = "96024")] |
| pub fn would_be_satisfied_by_ref_of<T>(&self) -> bool |
| where |
| T: ?Sized + 'static, |
| { |
| self.would_be_satisfied_by::<tags::Ref<tags::MaybeSizedValue<T>>>() |
| } |
| |
| fn would_be_satisfied_by<I>(&self) -> bool |
| where |
| I: tags::Type<'a>, |
| { |
| matches!(self.0.downcast::<I>(), Some(TaggedOption(None))) |
| } |
| } |
| |
| #[unstable(feature = "provide_any", issue = "96024")] |
| impl<'a> fmt::Debug for Demand<'a> { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Demand").finish_non_exhaustive() |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Type tags |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| mod tags { |
| //! Type tags are used to identify a type using a separate value. This module includes type tags |
| //! for some very common types. |
| //! |
| //! Currently type tags are not exposed to the user. But in the future, if you want to use the |
| //! Provider API with more complex types (typically those including lifetime parameters), you |
| //! will need to write your own tags. |
| |
| use crate::marker::PhantomData; |
| |
| /// This trait is implemented by specific tag types in order to allow |
| /// describing a type which can be requested for a given lifetime `'a`. |
| /// |
| /// A few example implementations for type-driven tags can be found in this |
| /// module, although crates may also implement their own tags for more |
| /// complex types with internal lifetimes. |
| pub trait Type<'a>: Sized + 'static { |
| /// The type of values which may be tagged by this tag for the given |
| /// lifetime. |
| type Reified: 'a; |
| } |
| |
| /// Similar to the [`Type`] trait, but represents a type which may be unsized (i.e., has a |
| /// `?Sized` bound). E.g., `str`. |
| pub trait MaybeSizedType<'a>: Sized + 'static { |
| type Reified: 'a + ?Sized; |
| } |
| |
| impl<'a, T: Type<'a>> MaybeSizedType<'a> for T { |
| type Reified = T::Reified; |
| } |
| |
| /// Type-based tag for types bounded by `'static`, i.e., with no borrowed elements. |
| #[derive(Debug)] |
| pub struct Value<T: 'static>(PhantomData<T>); |
| |
| impl<'a, T: 'static> Type<'a> for Value<T> { |
| type Reified = T; |
| } |
| |
| /// Type-based tag similar to [`Value`] but which may be unsized (i.e., has a `?Sized` bound). |
| #[derive(Debug)] |
| pub struct MaybeSizedValue<T: ?Sized + 'static>(PhantomData<T>); |
| |
| impl<'a, T: ?Sized + 'static> MaybeSizedType<'a> for MaybeSizedValue<T> { |
| type Reified = T; |
| } |
| |
| /// Type-based tag for reference types (`&'a T`, where T is represented by |
| /// `<I as MaybeSizedType<'a>>::Reified`. |
| #[derive(Debug)] |
| pub struct Ref<I>(PhantomData<I>); |
| |
| impl<'a, I: MaybeSizedType<'a>> Type<'a> for Ref<I> { |
| type Reified = &'a I::Reified; |
| } |
| } |
| |
| /// An `Option` with a type tag `I`. |
| /// |
| /// Since this struct implements `Erased`, the type can be erased to make a dynamically typed |
| /// option. The type can be checked dynamically using `Erased::tag_id` and since this is statically |
| /// checked for the concrete type, there is some degree of type safety. |
| #[repr(transparent)] |
| struct TaggedOption<'a, I: tags::Type<'a>>(Option<I::Reified>); |
| |
| impl<'a, I: tags::Type<'a>> TaggedOption<'a, I> { |
| fn as_demand(&mut self) -> &mut Demand<'a> { |
| Demand::new(self as &mut (dyn Erased<'a> + 'a)) |
| } |
| } |
| |
| /// Represents a type-erased but identifiable object. |
| /// |
| /// This trait is exclusively implemented by the `TaggedOption` type. |
| unsafe trait Erased<'a>: 'a { |
| /// The `TypeId` of the erased type. |
| fn tag_id(&self) -> TypeId; |
| } |
| |
| unsafe impl<'a, I: tags::Type<'a>> Erased<'a> for TaggedOption<'a, I> { |
| fn tag_id(&self) -> TypeId { |
| TypeId::of::<I>() |
| } |
| } |
| |
| #[unstable(feature = "provide_any", issue = "96024")] |
| impl<'a> dyn Erased<'a> + 'a { |
| /// Returns some reference to the dynamic value if it is tagged with `I`, |
| /// or `None` otherwise. |
| #[inline] |
| fn downcast<I>(&self) -> Option<&TaggedOption<'a, I>> |
| where |
| I: tags::Type<'a>, |
| { |
| if self.tag_id() == TypeId::of::<I>() { |
| // SAFETY: Just checked whether we're pointing to an I. |
| Some(unsafe { &*(self as *const Self).cast::<TaggedOption<'a, I>>() }) |
| } else { |
| None |
| } |
| } |
| |
| /// Returns some mutable reference to the dynamic value if it is tagged with `I`, |
| /// or `None` otherwise. |
| #[inline] |
| fn downcast_mut<I>(&mut self) -> Option<&mut TaggedOption<'a, I>> |
| where |
| I: tags::Type<'a>, |
| { |
| if self.tag_id() == TypeId::of::<I>() { |
| // SAFETY: Just checked whether we're pointing to an I. |
| Some(unsafe { &mut *(self as *mut Self).cast::<TaggedOption<'a, I>>() }) |
| } else { |
| None |
| } |
| } |
| } |