| //! impl bool {} |
| |
| use crate::marker::Destruct; |
| |
| impl bool { |
| /// Returns `Some(t)` if the `bool` is [`true`](../std/keyword.true.html), |
| /// or `None` otherwise. |
| /// |
| /// Arguments passed to `then_some` are eagerly evaluated; if you are |
| /// passing the result of a function call, it is recommended to use |
| /// [`then`], which is lazily evaluated. |
| /// |
| /// [`then`]: bool::then |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!(false.then_some(0), None); |
| /// assert_eq!(true.then_some(0), Some(0)); |
| /// ``` |
| /// |
| /// ``` |
| /// let mut a = 0; |
| /// let mut function_with_side_effects = || { a += 1; }; |
| /// |
| /// true.then_some(function_with_side_effects()); |
| /// false.then_some(function_with_side_effects()); |
| /// |
| /// // `a` is incremented twice because the value passed to `then_some` is |
| /// // evaluated eagerly. |
| /// assert_eq!(a, 2); |
| /// ``` |
| #[stable(feature = "bool_to_option", since = "1.62.0")] |
| #[rustc_const_unstable(feature = "const_bool_to_option", issue = "91917")] |
| #[inline] |
| pub const fn then_some<T>(self, t: T) -> Option<T> |
| where |
| T: ~const Destruct, |
| { |
| if self { Some(t) } else { None } |
| } |
| |
| /// Returns `Some(f())` if the `bool` is [`true`](../std/keyword.true.html), |
| /// or `None` otherwise. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// assert_eq!(false.then(|| 0), None); |
| /// assert_eq!(true.then(|| 0), Some(0)); |
| /// ``` |
| /// |
| /// ``` |
| /// let mut a = 0; |
| /// |
| /// true.then(|| { a += 1; }); |
| /// false.then(|| { a += 1; }); |
| /// |
| /// // `a` is incremented once because the closure is evaluated lazily by |
| /// // `then`. |
| /// assert_eq!(a, 1); |
| /// ``` |
| #[stable(feature = "lazy_bool_to_option", since = "1.50.0")] |
| #[rustc_const_unstable(feature = "const_bool_to_option", issue = "91917")] |
| #[inline] |
| pub const fn then<T, F>(self, f: F) -> Option<T> |
| where |
| F: ~const FnOnce() -> T, |
| F: ~const Destruct, |
| { |
| if self { Some(f()) } else { None } |
| } |
| } |