From cdb1a799f8793c4c858abc05b437fa2e569f51e6 Mon Sep 17 00:00:00 2001 From: Scott McMurray <scottmcm@users.noreply.github.com> Date: Sat, 17 Nov 2018 00:31:34 -0800 Subject: [PATCH] Add VecDeque::resize_with --- src/liballoc/collections/vec_deque.rs | 40 ++++++++++++++++++++++++++- 1 file changed, 39 insertions(+), 1 deletion(-) diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs index 88e76033f273e..cbf104a8fcde9 100644 --- a/src/liballoc/collections/vec_deque.rs +++ b/src/liballoc/collections/vec_deque.rs @@ -19,7 +19,7 @@ use core::cmp::Ordering; use core::fmt; -use core::iter::{repeat, FromIterator, FusedIterator}; +use core::iter::{repeat, repeat_with, FromIterator, FusedIterator}; use core::mem; use core::ops::Bound::{Excluded, Included, Unbounded}; use core::ops::{Index, IndexMut, RangeBounds}; @@ -1920,6 +1920,44 @@ impl<T: Clone> VecDeque<T> { self.truncate(new_len); } } + + /// Modifies the `VecDeque` in-place so that `len()` is equal to `new_len`, + /// either by removing excess elements from the back or by appending + /// elements generated by calling `generator` to the back. + /// + /// # Examples + /// + /// ``` + /// #![feature(vec_resize_with)] + /// + /// use std::collections::VecDeque; + /// + /// let mut buf = VecDeque::new(); + /// buf.push_back(5); + /// buf.push_back(10); + /// buf.push_back(15); + /// assert_eq!(buf, [5, 10, 15]); + /// + /// buf.resize_with(5, Default::default); + /// assert_eq!(buf, [5, 10, 15, 0, 0]); + /// + /// buf.resize_with(2, || unreachable!()); + /// assert_eq!(buf, [5, 10]); + /// + /// let mut state = 100; + /// buf.resize_with(5, || { state += 1; state }); + /// assert_eq!(buf, [5, 10, 101, 102, 103]); + /// ``` + #[unstable(feature = "vec_resize_with", issue = "41758")] + pub fn resize_with(&mut self, new_len: usize, generator: impl FnMut()->T) { + let len = self.len(); + + if new_len > len { + self.extend(repeat_with(generator).take(new_len - len)) + } else { + self.truncate(new_len); + } + } } /// Returns the index in the underlying buffer for a given logical element index.