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More practical examples for Option::and_then

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cyqsimon 2022-02-10 16:09:49 +08:00
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21
library/core/src/option.rs
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@ -1207,13 +1207,22 @@ impl<T> Option<T> {
/// # Examples /// # Examples
/// ///
/// ``` /// ```
/// fn sq(x: u32) -> Option<u32> { Some(x * x) } /// fn squared_string(x: u32) -> Option<String> { Some((x * x).to_string()) }
/// fn nope(_: u32) -> Option<u32> { None }
/// ///
/// assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16)); /// assert_eq!(Some(2).and_then(squared_string), Some(4.to_string()));
/// assert_eq!(Some(2).and_then(sq).and_then(nope), None); /// assert_eq!(None.and_then(squared_string), None);
/// assert_eq!(Some(2).and_then(nope).and_then(sq), None); /// ```
/// assert_eq!(None.and_then(sq).and_then(sq), None); ///
/// Often used to chain fallible operations that may return [`None`].
///
/// ```
/// let arr_2d = [["A1", "A2"], ["B1", "B2"]];
///
/// let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
/// assert_eq!(item_0_1, Some(&"A2"));
///
/// let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
/// assert_eq!(item_2_0, None);
/// ``` /// ```
#[inline] #[inline]
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]