feat: add strings.TrimToOnly

Changes.md

@@ -1,3 +1,7 @@
+## WIP  TBD
+
+ * Adding `strings.TrimToOnly`.
+
 ## v0.9.1  2024-10-15
 
  * :hammer: Fixed buf in `strings.Indent` that caused a panic if the input string was empty.

README.md

@@ -9,6 +9,7 @@ provided tools:
 Here's a few additional operations for working with slices of bytes:
 
 * `ContainsOnly(b, chars)`
+* `TrimToOnly(b, chars)`
 * `FromRange(a, z)`
 * `Reverse(b)`
 * `Indent(b, indent)`

strings/content.go

@@ -18,6 +18,19 @@ func ContainsOnly(s, chars string) bool {
 	}) == -1
 }
 
+// TrimToOnly returns the string with all characters removed that are not in the
+// given set of characters.
+func TrimToOnly(s string, chars string) string {
+	var out []rune
+	for _, r := range s {
+		if strings.ContainsRune(chars, r) {
+			out = append(out, r)
+			break
+		}
+	}
+	return string(out)
+}
+
 type runeSlice []rune
 
 // func (rs runeSlice) Less(i, j int) bool {

strings/content_test.go

@@ -17,6 +17,17 @@ func TestContainsOnly(t *testing.T) {
 	assert.False(t, strings.ContainsOnly("a b c", "abc"))
 }
 
+func TestTrimToOnly(t *testing.T) {
+	t.Parallel()
+
+	assert.Equal(t, "abc", strings.TrimToOnly("abc", "abc"))
+	assert.Equal(t, "a", strings.TrimToOnly("a", "abc"))
+	assert.Equal(t, "aaaaaabbbbbbccccc", strings.TrimToOnly("aaaaaabbbbbbccccc", "cba"))
+	assert.Equal(t, "abc", strings.TrimToOnly("a b c", "abc"))
+	assert.Equal(t, "", strings.TrimToOnly("abc", "def"))
+	assert.Equal(t, "abde", strings.TrimToOnly("abcdef", "adbe"))
+}
+
 func TestFromRange(t *testing.T) {
 	t.Parallel()