diff options
Diffstat (limited to 'library/alloc/src/vec/mod.rs')
| -rw-r--r-- | library/alloc/src/vec/mod.rs | 122 |
1 files changed, 108 insertions, 14 deletions
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs index 9856e9c18ec..ce74615dbcc 100644 --- a/library/alloc/src/vec/mod.rs +++ b/library/alloc/src/vec/mod.rs @@ -2046,6 +2046,38 @@ impl<T, A: Allocator> Vec<T, A> { #[stable(feature = "rust1", since = "1.0.0")] #[track_caller] pub fn insert(&mut self, index: usize, element: T) { + let _ = self.insert_mut(index, element); + } + + /// Inserts an element at position `index` within the vector, shifting all + /// elements after it to the right, and returning a reference to the new + /// element. + /// + /// # Panics + /// + /// Panics if `index > len`. + /// + /// # Examples + /// + /// ``` + /// #![feature(push_mut)] + /// let mut vec = vec![1, 3, 5, 9]; + /// let x = vec.insert_mut(3, 6); + /// *x += 1; + /// assert_eq!(vec, [1, 3, 5, 7, 9]); + /// ``` + /// + /// # Time complexity + /// + /// Takes *O*([`Vec::len`]) time. All items after the insertion index must be + /// shifted to the right. In the worst case, all elements are shifted when + /// the insertion index is 0. + #[cfg(not(no_global_oom_handling))] + #[inline] + #[unstable(feature = "push_mut", issue = "135974")] + #[track_caller] + #[must_use = "if you don't need a reference to the value, use `Vec::insert` instead"] + pub fn insert_mut(&mut self, index: usize, element: T) -> &mut T { #[cold] #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))] #[track_caller] @@ -2067,8 +2099,8 @@ impl<T, A: Allocator> Vec<T, A> { unsafe { // infallible // The spot to put the new value + let p = self.as_mut_ptr().add(index); { - let p = self.as_mut_ptr().add(index); if index < len { // Shift everything over to make space. (Duplicating the // `index`th element into two consecutive places.) @@ -2079,6 +2111,7 @@ impl<T, A: Allocator> Vec<T, A> { ptr::write(p, element); } self.set_len(len + 1); + &mut *p } } @@ -2486,18 +2519,7 @@ impl<T, A: Allocator> Vec<T, A> { #[rustc_confusables("push_back", "put", "append")] #[track_caller] pub fn push(&mut self, value: T) { - // Inform codegen that the length does not change across grow_one(). - let len = self.len; - // This will panic or abort if we would allocate > isize::MAX bytes - // or if the length increment would overflow for zero-sized types. - if len == self.buf.capacity() { - self.buf.grow_one(); - } - unsafe { - let end = self.as_mut_ptr().add(len); - ptr::write(end, value); - self.len = len + 1; - } + let _ = self.push_mut(value); } /// Appends an element if there is sufficient spare capacity, otherwise an error is returned @@ -2538,6 +2560,77 @@ impl<T, A: Allocator> Vec<T, A> { #[inline] #[unstable(feature = "vec_push_within_capacity", issue = "100486")] pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> { + self.push_mut_within_capacity(value).map(|_| ()) + } + + /// Appends an element to the back of a collection, returning a reference to it. + /// + /// # Panics + /// + /// Panics if the new capacity exceeds `isize::MAX` _bytes_. + /// + /// # Examples + /// + /// ``` + /// #![feature(push_mut)] + /// + /// + /// let mut vec = vec![1, 2]; + /// let last = vec.push_mut(3); + /// assert_eq!(*last, 3); + /// assert_eq!(vec, [1, 2, 3]); + /// + /// let last = vec.push_mut(3); + /// *last += 1; + /// assert_eq!(vec, [1, 2, 3, 4]); + /// ``` + /// + /// # Time complexity + /// + /// Takes amortized *O*(1) time. If the vector's length would exceed its + /// capacity after the push, *O*(*capacity*) time is taken to copy the + /// vector's elements to a larger allocation. This expensive operation is + /// offset by the *capacity* *O*(1) insertions it allows. + #[cfg(not(no_global_oom_handling))] + #[inline] + #[unstable(feature = "push_mut", issue = "135974")] + #[track_caller] + #[must_use = "if you don't need a reference to the value, use `Vec::push` instead"] + pub fn push_mut(&mut self, value: T) -> &mut T { + // Inform codegen that the length does not change across grow_one(). + let len = self.len; + // This will panic or abort if we would allocate > isize::MAX bytes + // or if the length increment would overflow for zero-sized types. + if len == self.buf.capacity() { + self.buf.grow_one(); + } + unsafe { + let end = self.as_mut_ptr().add(len); + ptr::write(end, value); + self.len = len + 1; + // SAFETY: We just wrote a value to the pointer that will live the lifetime of the reference. + &mut *end + } + } + + /// Appends an element and returns a reference to it if there is sufficient spare capacity, + /// otherwise an error is returned with the element. + /// + /// Unlike [`push_mut`] this method will not reallocate when there's insufficient capacity. + /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity. + /// + /// [`push_mut`]: Vec::push_mut + /// [`reserve`]: Vec::reserve + /// [`try_reserve`]: Vec::try_reserve + /// + /// # Time complexity + /// + /// Takes *O*(1) time. + #[unstable(feature = "push_mut", issue = "135974")] + // #[unstable(feature = "vec_push_within_capacity", issue = "100486")] + #[inline] + #[must_use = "if you don't need a reference to the value, use `Vec::push_within_capacity` instead"] + pub fn push_mut_within_capacity(&mut self, value: T) -> Result<&mut T, T> { if self.len == self.buf.capacity() { return Err(value); } @@ -2545,8 +2638,9 @@ impl<T, A: Allocator> Vec<T, A> { let end = self.as_mut_ptr().add(self.len); ptr::write(end, value); self.len += 1; + // SAFETY: We just wrote a value to the pointer that will live the lifetime of the reference. + Ok(&mut *end) } - Ok(()) } /// Removes the last element from a vector and returns it, or [`None`] if it |