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Add documentation for string->Cow conversions

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Mostly, it's just to reassure everyone that these functions don't allocate.

Part of #51430
This commit is contained in:
Michael Howell 2021-03-02 16:37:50 -07:00
parent 8fd946c63a
commit 69a37a63fa
1 changed files with 33 additions and 0 deletions
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33
library/alloc/src/string.rs
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@ -2352,6 +2352,16 @@ fn from(s: Cow<'a, str>) -> String {
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<&'a str> for Cow<'a, str> {
/// Converts a string slice into a Borrowed variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));
/// ```
#[inline]
fn from(s: &'a str) -> Cow<'a, str> {
Cow::Borrowed(s)
@ -2360,6 +2370,18 @@ fn from(s: &'a str) -> Cow<'a, str> {
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<String> for Cow<'a, str> {
/// Converts a String into an Owned variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// let s = "eggplant".to_string();
/// let s2 = "eggplant".to_string();
/// assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));
/// ```
#[inline]
fn from(s: String) -> Cow<'a, str> {
Cow::Owned(s)
@ -2368,6 +2390,17 @@ fn from(s: String) -> Cow<'a, str> {
#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
impl<'a> From<&'a String> for Cow<'a, str> {
/// Converts a String reference into a Borrowed variant.
/// No heap allocation is performed, and the string
/// is not copied.
///
/// # Example
///
/// ```
/// # use std::borrow::Cow;
/// let s = "eggplant".to_string();
/// assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));
/// ```
#[inline]
fn from(s: &'a String) -> Cow<'a, str> {
Cow::Borrowed(s.as_str())