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slices: add in-place Reverse function

Fixes #58565

Change-Id: I583f8380c12386178fb18e553322bbb019d9fae0
Reviewed-on: https://go-review.googlesource.com/c/go/+/468855
Run-TryBot: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Shay Nehmad <dude500@gmail.com>
This commit is contained in:
Alan Donovan 2023-02-16 11:02:12 -05:00
parent 58d40d156e
commit 3ca52f4c31
4 changed files with 46 additions and 0 deletions

1
api/next/58565.txt Normal file
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@ -0,0 +1 @@
pkg slices, func Reverse[$0 interface{}]([]$0) #58565

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@ -668,6 +668,16 @@ Do not send CLs removing the interior tags from such phrases.
</dd>
</dl><!-- spec -->
<dl id="slices"><dt><a href="/pkg/slices/">slices</a></dt>
<dd>
<p><!-- https://go.dev/issue/45955 -->
The new <a href="/pkg/slices/"><code>slices</code></a> package
provides many common operations on slices, using generic
functions that work with slices of any element type.
</p>
</dd>
</dl>
<dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
<dd>
<p><!-- https://go.dev/issue/56102, CL 451356 -->

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@ -445,3 +445,10 @@ func startIdx[S ~[]E, E any](haystack, needle S) int {
// TODO: what if the overlap is by a non-integral number of Es?
panic("needle not found")
}
// Reverse reverses the elements of the slice in place.
func Reverse[E any](s []E) {
for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
s[i], s[j] = s[j], s[i]
}
}

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@ -623,6 +623,34 @@ func TestClip(t *testing.T) {
}
}
func TestReverse(t *testing.T) {
even := []int{3, 1, 4, 1, 5, 9} // len = 6
Reverse(even)
if want := []int{9, 5, 1, 4, 1, 3}; !Equal(even, want) {
t.Errorf("Reverse(even) = %v, want %v", even, want)
}
odd := []int{3, 1, 4, 1, 5, 9, 2} // len = 7
Reverse(odd)
if want := []int{2, 9, 5, 1, 4, 1, 3}; !Equal(odd, want) {
t.Errorf("Reverse(odd) = %v, want %v", odd, want)
}
words := strings.Fields("one two three")
Reverse(words)
if want := strings.Fields("three two one"); !Equal(words, want) {
t.Errorf("Reverse(words) = %v, want %v", words, want)
}
singleton := []string{"one"}
Reverse(singleton)
if want := []string{"one"}; !Equal(singleton, want) {
t.Errorf("Reverse(singeleton) = %v, want %v", singleton, want)
}
Reverse[string](nil)
}
// naiveReplace is a baseline implementation to the Replace function.
func naiveReplace[S ~[]E, E any](s S, i, j int, v ...E) S {
s = Delete(s, i, j)