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

4 files changed, 79 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;
+		}
+	}
+}
diff --git a/src/pkg/strings/strings.go b/src/pkg/strings/strings.go
index 055d7d1e99..7ccfc5ca84 100644
--- a/src/pkg/strings/strings.go
+++ b/src/pkg/strings/strings.go
@@ -188,6 +188,20 @@ func Map(mapping func(rune int) int, s string) string {
 	return string(b[0:nbytes]);
 }
 
+// Repeat returns a new string consisting of count copies of the string s.
+func Repeat(s string, count int) string {
+	b := make([]byte, len(s)*count);
+	bp := 0;
+	for i := 0; i < count; i++ {
+		for j := 0; j < len(s); j++ {
+			b[bp] = s[j];
+			bp++;
+		}
+	}
+	return string(b);
+}
+
+
 // ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
 func ToUpper(s string) string	{ return Map(unicode.ToUpper, s) }
 
diff --git a/src/pkg/strings/strings_test.go b/src/pkg/strings/strings_test.go
index 732da42421..0073f0d0ea 100644
--- a/src/pkg/strings/strings_test.go
+++ b/src/pkg/strings/strings_test.go
@@ -336,3 +336,28 @@ func TestCaseConsistency(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 {
+		a := Repeat(tt.in, tt.count);
+		if !equal("Repeat(s)", a, tt.out, t) {
+			t.Errorf("Repeat(%v, %d) = %v; want %v", tt.in, tt.count, a, tt.out);
+			continue;
+		}
+	}
+}