slices: add DeleteFunc

Fixes golang#54768

Change-Id: I588ae33c13e0bbd9d324c11771667b22a864047d
Reviewed-on: https://go-review.googlesource.com/c/go/+/483175
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Eli Bendersky <eliben@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

api/next/54768.txt

@@ -0,0 +1 @@
+pkg slices, func DeleteFunc[$0 interface{ ~[]$1 }, $1 interface{}]($0, func($1) bool) $0 #54768

src/slices/slices.go

@@ -109,6 +109,32 @@ func Delete[S ~[]E, E any](s S, i, j int) S {
  return append(s[:i], s[j:]...)
 }
 
+// DeleteFunc removes any elements from s for which del returns true,
+// returning the modified slice.
+// DeleteFunc modifies the contents of the slice s;
+// it does not create a new slice.
+// When DeleteFunc removes m elements, it might not modify the elements
+// s[len(s)-m:len(s)]. If those elements contain pointers you might consider
+// zeroing those elements so that objects they reference can be garbage
+// collected.
+func DeleteFunc[S ~[]E, E any](s S, del func(E) bool) S {
+ // Don't start copying elements until we find one to delete.
+ for i, v := range s {
+ if del(v) {
+ j := i
+ for i++; i < len(s); i++ {
+ v = s[i]
+ if !del(v) {
+ s[j] = v
+ j++
+ }
+ }
+ return s[:j]
+ }
+ }
+ return 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.
 func Replace[S ~[]E, E any](s S, i, j int, v ...E) S {

src/slices/slices_test.go

@@ -304,6 +304,52 @@ func TestDelete(t *testing.T) {
  }
 }
 
+var deleteFuncTests = []struct {
+ s []int
+ fn func(int) bool
+ want []int
+}{
+ {
+ nil,
+ func(int) bool { return true },
+ nil,
+ },
+ {
+ []int{1, 2, 3},
+ func(int) bool { return true },
+ nil,
+ },
+ {
+ []int{1, 2, 3},
+ func(int) bool { return false },
+ []int{1, 2, 3},
+ },
+ {
+ []int{1, 2, 3},
+ func(i int) bool { return i > 2 },
+ []int{1, 2},
+ },
+ {
+ []int{1, 2, 3},
+ func(i int) bool { return i < 2 },
+ []int{2, 3},
+ },
+ {
+ []int{10, 2, 30},
+ func(i int) bool { return i >= 10 },
+ []int{2},
+ },
+}
+
+func TestDeleteFunc(t *testing.T) {
+ for i, test := range deleteFuncTests {
+ copy := Clone(test.s)
+ if got := DeleteFunc(copy, test.fn); !Equal(got, test.want) {
+ t.Errorf("DeleteFunc case %d: got %v, want %v", i, got, test.want)
+ }
+ }
+}
+
 func panics(f func()) (b bool) {
  defer func() {
  if x := recover(); x != nil {