Support Stringer for MapIter

Author: BooleanCat

iter/map.go

@@ -1,6 +1,11 @@
 package iter
 
-import "github.com/BooleanCat/go-functional/option"
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/BooleanCat/go-functional/option"
+)
 
 // MapIter iterator, see [Map].
 type MapIter[T, U any] struct {
@@ -47,4 +52,13 @@ func (iter *MapIter[T, U]) Next() option.Option[U] {
 	return option.Some(iter.fun(value))
 }
 
-var _ Iterator[struct{}] = new(MapIter[struct{}, struct{}])
+// String implements the [fmt.Stringer] interface
+func (iter MapIter[T, U]) String() string {
+	var instanceOfU U
+	return fmt.Sprintf("Iterator<Map, type=%s>", reflect.TypeOf(instanceOfU))
+}
+
+var (
+	_ fmt.Stringer       = new(MapIter[struct{}, struct{}])
+	_ Iterator[struct{}] = new(MapIter[struct{}, struct{}])
+)

iter/map_test.go

@@ -2,6 +2,7 @@ package iter_test
 
 import (
 	"fmt"
+	"strconv"
 	"testing"
 
 	"github.com/BooleanCat/go-functional/internal/assert"
@@ -26,6 +27,11 @@ func ExampleTransform() {
 	// Output: [2 3 4]
 }
 
+func ExampleMapIter_String() {
+	fmt.Println(iter.Map[int, string](iter.Count(), strconv.Itoa))
+	// Output: Iterator<Map, type=string>
+}
+
 func ExampleTransform_method() {
 	addTwo := func(number int) int { return number + 2 }
 	numbers := iter.Count().Transform(addTwo).Take(3).Collect()
@@ -61,3 +67,11 @@ func TestTransform(t *testing.T) {
 
 	assert.SliceEqual[int](t, numbers, []int{2, 3, 4})
 }
+
+func TestMapIter_String(t *testing.T) {
+	assert.Equal(
+		t,
+		iter.Map[int, string](iter.Count(), strconv.Itoa).String(),
+		"Iterator<Map, type=string>",
+	)
+}