An asked-for-in #go-nuts extension to quickly create a repeated

	copy of a string or a byte array.
        strings.Repeat("-", 50)
	bytes.Repeat(b, 99)

R=rsc
https://golang.org/cl/155063

2 files changed, 40 insertions, 0 deletions

diff --git a/src/pkg/bytes/bytes.go b/src/pkg/bytes/bytes.go
index f6cae73537..0c585bd80f 100644
--- a/src/pkg/bytes/bytes.go
+++ b/src/pkg/bytes/bytes.go
@@ -239,6 +239,19 @@ func Map(mapping func(rune int) int, s []byte) []byte {
 	return b[0:nbytes];
 }
 
+// Repeat returns a new byte array consisting of count copies of b.
+func Repeat(b []byte, count int) []byte {
+	nb := make([]byte, len(b)*count);
+	bp := 0;
+	for i := 0; i < count; i++ {
+		for j := 0; j < len(b); j++ {
+			nb[bp] = b[j];
+			bp++;
+		}
+	}
+	return nb;
+}
+
 // ToUpper returns a copy of the byte array s with all Unicode letters mapped to their upper case.
 func ToUpper(s []byte) []byte	{ return Map(unicode.ToUpper, s) }
 
diff --git a/src/pkg/bytes/bytes_test.go b/src/pkg/bytes/bytes_test.go
index dddaf5064e..3e737cb376 100644
--- a/src/pkg/bytes/bytes_test.go
+++ b/src/pkg/bytes/bytes_test.go
@@ -361,3 +361,30 @@ func TestAddByte(t *testing.T) {
 		}
 	}
 }
+
+type RepeatTest struct {
+	in, out	string;
+	count	int;
+}
+
+var RepeatTests = []RepeatTest{
+	RepeatTest{"", "", 0},
+	RepeatTest{"", "", 1},
+	RepeatTest{"", "", 2},
+	RepeatTest{"-", "", 0},
+	RepeatTest{"-", "-", 1},
+	RepeatTest{"-", "----------", 10},
+	RepeatTest{"abc ", "abc abc abc ", 3},
+}
+
+func TestRepeat(t *testing.T) {
+	for _, tt := range RepeatTests {
+		tin := strings.Bytes(tt.in);
+		tout := strings.Bytes(tt.out);
+		a := Repeat(tin, tt.count);
+		if !Equal(a, tout) {
+			t.Errorf("Repeat(%q, %d) = %q; want %q", tin, tt.count, a, tout);
+			continue;
+		}
+	}
+}