Add IndexOf for iter.Seq

iter/find_go123.go

@@ -0,0 +1,19 @@
+//go:build go1.23
+
+package iter
+
+// IndexOf returns the index at which the first occurrence of a value is found in a sequence or return -1
+// if the value cannot be found.
+func IndexOf[T comparable](delegate func(func(T) bool), element T) int {
+	index := 0
+
+	for item := range delegate {
+		if item == element {
+			return index
+		}
+
+		index++
+	}
+
+	return -1
+}

iter/find_go123_test.go

@@ -0,0 +1,29 @@
+//go:build go1.23
+
+package iter_test
+
+import (
+	"fmt"
+	"slices"
+	"testing"
+
+	li "github.com/samber/lo/iter"
+	"github.com/stretchr/testify/assert"
+)
+
+func ExampleIndexOf() {
+	numbers := slices.Values([]int{0, 1, 2, 1, 2, 3})
+	fmt.Println(li.IndexOf(numbers, 1))
+	// Output: 1
+}
+
+func TestIndexOf(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	result1 := li.IndexOf(slices.Values([]int{0, 1, 2, 1, 2, 3}), 2)
+	result2 := li.IndexOf(slices.Values([]int{0, 1, 2, 1, 2, 3}), 6)
+
+	is.Equal(result1, 2)
+	is.Equal(result2, -1)
+}

iter/iter.go

@@ -0,0 +1 @@
+package iter