1 | //! impl bool {} |
2 | |
3 | impl 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 | #[stable (feature = "lazy_bool_to_option" , since = "1.50.0" )] |
58 | #[inline ] |
59 | pub fn then<T, F: FnOnce() -> T>(self, f: F) -> Option<T> { |
60 | if self { Some(f()) } else { None } |
61 | } |
62 | } |
63 | |