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Rollup merge of #80834 - bugadani:vecdeque, r=oli-obk

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Remove unreachable panics from VecDeque::{front/back}[_mut]

`VecDeque`'s `front`, `front_mut`, `back` and `back_mut` methods are implemented in terms of the index operator, which causes these functions to contain [unreachable panic calls](https://rust.godbolt.org/z/MTnq1o).

This PR reimplements these methods in terms of `get[_mut]` instead.
This commit is contained in:
Yuki Okushi 2021-01-15 18:26:11 +09:00 • committed by GitHub
commit 1b8fd02daa
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2 changed files with 23 additions and 5 deletions
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9
library/alloc/src/collections/vec_deque/mod.rs
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@ -1292,7 +1292,7 @@ impl<T> VecDeque<T> {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn front(&self) -> Option<&T> {
if !self.is_empty() { Some(&self[0]) } else { None }
self.get(0)
}
/// Provides a mutable reference to the front element, or `None` if the
@ -1316,7 +1316,7 @@ impl<T> VecDeque<T> {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn front_mut(&mut self) -> Option<&mut T> {
if !self.is_empty() { Some(&mut self[0]) } else { None }
self.get_mut(0)
}
/// Provides a reference to the back element, or `None` if the `VecDeque` is
@ -1336,7 +1336,7 @@ impl<T> VecDeque<T> {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn back(&self) -> Option<&T> {
if !self.is_empty() { Some(&self[self.len() - 1]) } else { None }
self.get(self.len().wrapping_sub(1))
}
/// Provides a mutable reference to the back element, or `None` if the
@ -1360,8 +1360,7 @@ impl<T> VecDeque<T> {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn back_mut(&mut self) -> Option<&mut T> {
let len = self.len();
if !self.is_empty() { Some(&mut self[len - 1]) } else { None }
self.get_mut(self.len().wrapping_sub(1))
}
/// Removes the first element and returns it, or `None` if the `VecDeque` is