slices: update doc for Delete and Replace

Fixes #64013

Change-Id: Ibaeaad6120bff041bf6ab80fd4cd613f7d4ac5a7
GitHub-Last-Rev: 647ed646ec7c2e4ce93c5d3847d0b9e3627d7497
GitHub-Pull-Request: golang/go#64024
Reviewed-on: https://go-review.googlesource.com/c/go/+/540955
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Jes Cok <xigua67damn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Eli Bendersky <eliben@google.com>

diff --git a/src/slices/slices.go b/src/slices/slices.go
index fe50a91d4844f38e517926f7e390126c218c64b0..4c398557ff4241565f5ac776d28561cc53913abb 100644 (file)
--- a/src/slices/slices.go
+++ b/src/slices/slices.go
@@ -212,7 +212,7 @@ func Insert[S ~[]E, E any](s S, i int, v ...E) S {
 }
 
 // Delete removes the elements s[i:j] from s, returning the modified slice.
-// Delete panics if s[i:j] is not a valid slice of s.
+// Delete panics if j > len(s) or s[i:j] is not a valid slice of s.
 // Delete is O(len(s)-j), so if many items must be deleted, it is better to
 // make a single call deleting them all together than to delete one at a time.
 // Delete might not modify the elements s[len(s)-(j-i):len(s)]. If those
@@ -246,9 +246,10 @@ func DeleteFunc[S ~[]E, E any](s S, del func(E) bool) S {
 }
 
 // Replace replaces the elements s[i:j] by the given v, and returns the
-// modified slice. Replace panics if s[i:j] is not a valid slice of s.
+// modified slice.
+// Replace panics if j > len(s) or s[i:j] is not a valid slice of s.
 func Replace[S ~[]E, E any](s S, i, j int, v ...E) S {
-       _ = s[i:j] // verify that i:j is a valid subslice
+       _ = s[i:j] // bounds check
 
        if i == j {
                return Insert(s, i, v...)

diff --git a/src/slices/slices_test.go b/src/slices/slices_test.go
index 7d4fc34b2e6bdbae2d6c52e14d11ad1acf7023b6..2fc583ff909d048738d70590c55e94a4207770cd 100644 (file)
--- a/src/slices/slices_test.go
+++ b/src/slices/slices_test.go
@@ -659,6 +659,10 @@ func panics(f func()) (b bool) {
 }
 
 func TestDeletePanics(t *testing.T) {
+       s := []int{0, 1, 2, 3, 4}
+       s = s[0:2]
+       _ = s[0:4] // this is a valid slice of s
+
        for _, test := range []struct {
                name string
                s    []int
@@ -669,6 +673,7 @@ func TestDeletePanics(t *testing.T) {
                {"with out-of-bounds first index", []int{42}, 2, 3},
                {"with out-of-bounds second index", []int{42}, 0, 2},
                {"with invalid i>j", []int{42}, 1, 0},
+               {"s[i:j] is valid and j > len(s)", s, 0, 4},
        } {
                if !panics(func() { Delete(test.s, test.i, test.j) }) {
                        t.Errorf("Delete %s: got no panic, want panic", test.name)
@@ -928,6 +933,10 @@ func TestReplace(t *testing.T) {
 }
 
 func TestReplacePanics(t *testing.T) {
+       s := []int{0, 1, 2, 3, 4}
+       s = s[0:2]
+       _ = s[0:4] // this is a valid slice of s
+
        for _, test := range []struct {
                name string
                s, v []int
@@ -936,6 +945,7 @@ func TestReplacePanics(t *testing.T) {
                {"indexes out of order", []int{1, 2}, []int{3}, 2, 1},
                {"large index", []int{1, 2}, []int{3}, 1, 10},
                {"negative index", []int{1, 2}, []int{3}, -1, 2},
+               {"s[i:j] is valid and j > len(s)", s, nil, 0, 4},
        } {
                ss, vv := Clone(test.s), Clone(test.v)
                if !panics(func() { Replace(ss, test.i, test.j, vv...) }) {