feat: add JoinFunc

slice/slice.go

@@ -1398,3 +1398,16 @@ func Frequency[T comparable](slice []T) map[T]int {
 
 	return result
 }
+
+// JoinFunc joins the slice elements into a single string with the given separator.
+// Play: todo
+func JoinFunc[T any](slice []T, sep string, transform func(T) T) string {
+	var buf strings.Builder
+	for i, v := range slice {
+		if i > 0 {
+			buf.WriteString(sep)
+		}
+		buf.WriteString(fmt.Sprint(transform(v)))
+	}
+	return buf.String()
+}

slice/slice_example_test.go

@@ -1261,3 +1261,14 @@ func ExampleFrequency() {
 	// Output:
 	// map[a:1 b:2 c:3]
 }
+
+func ExampleJoinFunc() {
+	result := JoinFunc([]string{"a", "b", "c"}, ", ", func(s string) string {
+		return strings.ToUpper(s)
+	})
+
+	fmt.Println(result)
+
+	// Output:
+	// A, B, C
+}

slice/slice_test.go

@@ -1816,3 +1816,43 @@ func TestFrequency(t *testing.T) {
 		assert.Equal(expected, result)
 	})
 }
+
+func TestJoinFunc(t *testing.T) {
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestJoinFunc")
+
+	t.Run("basic case", func(t *testing.T) {
+		result := JoinFunc([]int{1, 2, 3}, ", ", func(i int) int {
+			return i * 2
+		})
+
+		expected := "2, 4, 6"
+		assert.Equal(expected, result)
+	})
+
+	t.Run("empty slice", func(t *testing.T) {
+		result := JoinFunc([]int{}, ", ", func(i int) int {
+			return i * 2
+		})
+
+		assert.Equal("", result)
+	})
+
+	t.Run("single element slice", func(t *testing.T) {
+		result := JoinFunc([]int{1}, ", ", func(i int) int {
+			return i * 2
+		})
+
+		assert.Equal("2", result)
+	})
+
+	t.Run("string slice", func(t *testing.T) {
+		result := JoinFunc([]string{"a", "b", "c"}, ", ", func(s string) string {
+			return strings.ToUpper(s)
+		})
+
+		expected := "A, B, C"
+		assert.Equal(expected, result)
+	})
+}