Add CopyOf utility method

Add a utility method that returns a copy of a slice of strings.
This is primarily useful when appending to a string slice to avoid
accidentally reusing the backing array.

Test: util_test.go
Change-Id: I7801fc7ca19e27ddc9f1b1b452788b723c7f619c

2 files changed, 50 insertions, 0 deletions

diff --git a/android/util.go b/android/util.go
index 92ab845ba..8fc159dc8 100644
--- a/android/util.go
+++ b/android/util.go
@@ -20,6 +20,11 @@ import (
 	"strings"
 )
 
+// CopyOf returns a new slice that has the same contents as s.
+func CopyOf(s []string) []string {
+	return append([]string(nil), s...)
+}
+
 func JoinWithPrefix(strs []string, prefix string) string {
 	if len(strs) == 0 {
 		return ""
diff --git a/android/util_test.go b/android/util_test.go
index 1c791b240..2e5eb07ee 100644
--- a/android/util_test.go
+++ b/android/util_test.go
@@ -15,6 +15,7 @@
 package android
 
 import (
+	"fmt"
 	"reflect"
 	"testing"
 )
@@ -359,3 +360,47 @@ func TestRemoveFromList(t *testing.T) {
 		})
 	}
 }
+
+func ExampleCopyOf() {
+	a := []string{"1", "2", "3"}
+	b := CopyOf(a)
+	a[0] = "-1"
+	fmt.Printf("a = %q\n", a)
+	fmt.Printf("b = %q\n", b)
+
+	// Output:
+	// a = ["-1" "2" "3"]
+	// b = ["1" "2" "3"]
+}
+
+func ExampleCopyOf_append() {
+	a := make([]string, 1, 2)
+	a[0] = "foo"
+
+	fmt.Println("Without CopyOf:")
+	b := append(a, "bar")
+	c := append(a, "baz")
+	fmt.Printf("a = %q\n", a)
+	fmt.Printf("b = %q\n", b)
+	fmt.Printf("c = %q\n", c)
+
+	a = make([]string, 1, 2)
+	a[0] = "foo"
+
+	fmt.Println("With CopyOf:")
+	b = append(CopyOf(a), "bar")
+	c = append(CopyOf(a), "baz")
+	fmt.Printf("a = %q\n", a)
+	fmt.Printf("b = %q\n", b)
+	fmt.Printf("c = %q\n", c)
+
+	// Output:
+	// Without CopyOf:
+	// a = ["foo"]
+	// b = ["foo" "baz"]
+	// c = ["foo" "baz"]
+	// With CopyOf:
+	// a = ["foo"]
+	// b = ["foo" "bar"]
+	// c = ["foo" "baz"]
+}