feat: add IndexOf and LastIndexOf for stream

stream/stream.go

@@ -393,6 +393,26 @@ func (s Stream[T]) Min(less func(a, b T) bool) (T, bool) {
 	return min, true
 }
 
+// IndexOf returns the index of the first occurrence of the specified element in this stream, or -1 if this stream does not contain the element.
+func (s Stream[T]) IndexOf(target T, equal func(a, b T) bool) int {
+	for i, v := range s.source {
+		if equal(v, target) {
+			return i
+		}
+	}
+	return -1
+}
+
+// LastIndexOf returns the index of the last occurrence of the specified element in this stream, or -1 if this stream does not contain the element.
+func (s Stream[T]) LastIndexOf(target T, equal func(a, b T) bool) int {
+	for i := len(s.source) - 1; i >= 0; i-- {
+		if equal(s.source[i], target) {
+			return i
+		}
+	}
+	return -1
+}
+
 // ToSlice return the elements in the stream.
 // Play: https://go.dev/play/p/jI6_iZZuVFE
 func (s Stream[T]) ToSlice() []T {

stream/stream_example_test.go

@@ -384,3 +384,31 @@ func ExampleStream_Count() {
 	// 3
 	// 0
 }
+
+func ExampleStream_IndexOf() {
+	s := FromSlice([]int{1, 2, 3, 2})
+
+	result1 := s.IndexOf(0, func(a, b int) bool { return a == b })
+	result2 := s.IndexOf(2, func(a, b int) bool { return a == b })
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+
+	// Output:
+	// -1
+	// 1
+}
+
+func ExampleStream_LastIndexOf() {
+	s := FromSlice([]int{1, 2, 3, 2})
+
+	result1 := s.LastIndexOf(0, func(a, b int) bool { return a == b })
+	result2 := s.LastIndexOf(2, func(a, b int) bool { return a == b })
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+
+	// Output:
+	// -1
+	// 3
+}

stream/stream_test.go

@@ -381,3 +381,22 @@ func TestStream_Min(t *testing.T) {
 	assert.Equal(1, max)
 	assert.Equal(true, ok)
 }
+
+func TestStream_IndexOf(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_IndexOf")
+
+	s := FromSlice([]int{4, 2, 1, 3, 4})
+
+	assert.Equal(-1, s.IndexOf(0, func(a, b int) bool { return a == b }))
+	assert.Equal(0, s.IndexOf(4, func(a, b int) bool { return a == b }))
+	assert.Equal(3, s.IndexOf(3, func(a, b int) bool { return a == b }))
+}
+
+func TestStream_LastIndexOf(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_LastIndexOf")
+
+	s := FromSlice([]int{4, 2, 1, 3, 2})
+
+	assert.Equal(-1, s.LastIndexOf(0, func(a, b int) bool { return a == b }))
+	assert.Equal(4, s.LastIndexOf(2, func(a, b int) bool { return a == b }))
+}