diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go index 5d652e7179250..e802ee7421010 100644 --- a/src/reflect/all_test.go +++ b/src/reflect/all_test.go @@ -7298,6 +7298,48 @@ func TestMapIterNilMap(t *testing.T) { } } +func TestMapIterReset(t *testing.T) { + iter := new(MapIter) + + // Use of zero iterator should panic. + func() { + defer func() { recover() }() + iter.Next() + t.Fatal("Next did not panic") + }() + + // Reset to new Map should work. + m := map[string]int{"one": 1, "two": 2, "three": 3} + iter.Reset(ValueOf(m)) + if got, want := iterateToString(iter), `[one: 1, three: 3, two: 2]`; got != want { + t.Errorf("iterator returned %s (after sorting), want %s", got, want) + } + + // Reset to Zero value should work, but iterating over it should panic. + iter.Reset(Value{}) + func() { + defer func() { recover() }() + iter.Next() + t.Fatal("Next did not panic") + }() + + // Reset to a diferent Map with different types should work. + m2 := map[int]string{1: "one", 2: "two", 3: "three"} + iter.Reset(ValueOf(m2)) + if got, want := iterateToString(iter), `[1: one, 2: two, 3: three]`; got != want { + t.Errorf("iterator returned %s (after sorting), want %s", got, want) + } + + // Reset should not allocate. + n := int(testing.AllocsPerRun(10, func() { + iter.Reset(ValueOf(m2)) + iter.Reset(Value{}) + })) + if n > 0 { + t.Errorf("MapIter.Reset allocated %d times", n) + } +} + func TestMapIterSafety(t *testing.T) { // Using a zero MapIter causes a panic, but not a crash. func() { diff --git a/src/reflect/value.go b/src/reflect/value.go index f441fe92d9f5c..47db88dcecfa2 100644 --- a/src/reflect/value.go +++ b/src/reflect/value.go @@ -1698,6 +1698,17 @@ func (it *MapIter) Next() bool { return mapiterkey(it.it) != nil } +// Reset modifies it to iterate over v. +// It panics if v's Kind is not Map and v is not the zero Value. +func (it *MapIter) Reset(v Value) { + if v.IsValid() { + v.mustBe(Map) + } + it.m = v + it.it = nil + it.hiter = hiter{} +} + // MapRange returns a range iterator for a map. // It panics if v's Kind is not Map. //