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