core/
bool.rs

Help
1//! impl bool {}
2
3impl bool {
4    /// Returns `Some(t)` if the `bool` is [`true`](../std/keyword.true.html),
5    /// or `None` otherwise.
6    ///
7    /// Arguments passed to `then_some` are eagerly evaluated; if you are
8    /// passing the result of a function call, it is recommended to use
9    /// [`then`], which is lazily evaluated.
10    ///
11    /// [`then`]: bool::then
12    ///
13    /// # Examples
14    ///
15    /// ```
16    /// assert_eq!(false.then_some(0), None);
17    /// assert_eq!(true.then_some(0), Some(0));
18    /// ```
19    ///
20    /// ```
21    /// let mut a = 0;
22    /// let mut function_with_side_effects = || { a += 1; };
23    ///
24    /// true.then_some(function_with_side_effects());
25    /// false.then_some(function_with_side_effects());
26    ///
27    /// // `a` is incremented twice because the value passed to `then_some` is
28    /// // evaluated eagerly.
29    /// assert_eq!(a, 2);
30    /// ```
31    #[stable(feature = "bool_to_option", since = "1.62.0")]
32    #[inline]
33    pub fn then_some<T>(self, t: T) -> Option<T> {
34        if self { Some(t) } else { None }
35    }
36
37    /// Returns `Some(f())` if the `bool` is [`true`](../std/keyword.true.html),
38    /// or `None` otherwise.
39    ///
40    /// # Examples
41    ///
42    /// ```
43    /// assert_eq!(false.then(|| 0), None);
44    /// assert_eq!(true.then(|| 0), Some(0));
45    /// ```
46    ///
47    /// ```
48    /// let mut a = 0;
49    ///
50    /// true.then(|| { a += 1; });
51    /// false.then(|| { a += 1; });
52    ///
53    /// // `a` is incremented once because the closure is evaluated lazily by
54    /// // `then`.
55    /// assert_eq!(a, 1);
56    /// ```
57    #[doc(alias = "then_with")]
58    #[stable(feature = "lazy_bool_to_option", since = "1.50.0")]
59    #[rustc_diagnostic_item = "bool_then"]
60    #[inline]
61    pub fn then<T, F: FnOnce() -> T>(self, f: F) -> Option<T> {
62        if self { Some(f()) } else { None }
63    }
64}
core/bool.rs

core/
bool.rs
