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Add documentation on str::starts_with #120764

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merged 3 commits into from
Feb 10, 2024
Merged

Add documentation on str::starts_with #120764

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f0c6f5a
Add documentation on `str::starts_with`
vcfxb Feb 8, 2024
8ff1994
Fix whitespace issues that tidy caught
vcfxb Feb 8, 2024
d7263d7
Change wording
vcfxb Feb 10, 2024
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14 changes: 14 additions & 0 deletions library/core/src/str/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1160,6 +1160,12 @@ impl str {
/// The [pattern] can be a `&str`, [`char`], a slice of [`char`]s, or a
/// function or closure that determines if a character matches.
///
/// Note that there is a footgun to this method when using a slice of [`char`]s.
/// Some users may expect that a slice of chars will behave similarly to a `&str` with this method.
/// That is not currently the case. When you pass a slice of [`char`]s to this method, it will return true
/// if any of the [`char`]s in the slice is the first [`char`] of this string slice. It does not work for
/// sequentially comparing a slice of [`char`]s to a string slice. See the second example below.
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I don't think this wording (with "footgun", "some users", "currently", etc.) is very useful.

How about instead just adding a bit more detail to the paragraph above? Maybe something in this direction?

-    /// The [pattern] can be a `&str`, [`char`], a slice of [`char`]s, or a
-    /// function or closure that determines if a character matches.
+    /// The [pattern] can be a `&str` to check for a prefix,
+    /// or a [`char`], slice of [`char`]s, or function or closure 
+    /// to check the first character for a match.

///
/// [`char`]: prim@char
/// [pattern]: self::pattern
///
Expand All @@ -1171,6 +1177,14 @@ impl str {
/// assert!(bananas.starts_with("bana"));
/// assert!(!bananas.starts_with("nana"));
/// ```
///
/// ```
/// let bananas = "bananas";
///
/// // Note that both of these assert successfully.
/// assert!(bananas.starts_with(&['b', 'a', 'n', 'a']));
/// assert!(bananas.starts_with(&['a', 'b', 'c', 'd']));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn starts_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
pat.is_prefix_of(self)
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