feat: add reflect caller

Author: nrwiersma

src/reflect/all_test.go

@@ -3988,8 +3988,8 @@ func TestValuePanic(t *testing.T) {
 	shouldPanic("reflect.Value.Addr of unaddressable value", func() { vo(0).Addr() })
 	shouldPanic("call of reflect.Value.Bool on float64 Value", func() { vo(0.0).Bool() })
 	shouldPanic("call of reflect.Value.Bytes on string Value", func() { vo("").Bytes() })
-	shouldPanic("call of reflect.Value.Call on bool Value", func() { vo(true).Call(nil) })
-	shouldPanic("call of reflect.Value.CallSlice on int Value", func() { vo(0).CallSlice(nil) })
+	shouldPanic("call of reflect.Value.Caller on bool Value", func() { vo(true).Call(nil) })
+	shouldPanic("call of reflect.Value.Caller on int Value", func() { vo(0).CallSlice(nil) })
 	shouldPanic("call of reflect.Value.Close on string Value", func() { vo("").Close() })
 	shouldPanic("call of reflect.Value.Complex on float64 Value", func() { vo(0.0).Complex() })
 	shouldPanic("call of reflect.Value.Elem on bool Value", func() { vo(false).Elem() })
@@ -8408,3 +8408,19 @@ func TestClear(t *testing.T) {
 		})
 	}
 }
+
+func TestCaller_CallReusesOutValues(t *testing.T) {
+	fn := func() int {
+		return 27
+	}
+
+	var i int
+	v := ValueOf(&i).Elem()
+	out := []Value{v}
+
+	ValueOf(fn).Caller().Call([]Value{}, out)
+
+	if i != 27 {
+		t.Errorf("unexpected result for output value; got %d, want 27", i)
+	}
+}

src/reflect/benchmark_test.go

@@ -197,6 +197,19 @@ func BenchmarkCall(b *testing.B) {
 	})
 }
 
+func BenchmarkCallerCall(b *testing.B) {
+	fv := ValueOf(func(a, b string) {})
+	c := fv.Caller()
+	out := make([]Value, c.Type().NumOut())
+	b.ReportAllocs()
+	b.RunParallel(func(pb *testing.PB) {
+		args := []Value{ValueOf("a"), ValueOf("b")}
+		for pb.Next() {
+			c.Call(args, out)
+		}
+	})
+}
+
 type myint int64
 
 func (i *myint) inc() {
@@ -213,6 +226,17 @@ func BenchmarkCallMethod(b *testing.B) {
 	}
 }
 
+func BenchmarkCallerCallMethod(b *testing.B) {
+	b.ReportAllocs()
+	z := new(myint)
+
+	v := ValueOf(z.inc)
+	c := v.Caller()
+	for i := 0; i < b.N; i++ {
+		c.Call(nil, nil)
+	}
+}
+
 func BenchmarkCallArgCopy(b *testing.B) {
 	byteArray := func(n int) Value {
 		return Zero(ArrayOf(n, TypeOf(byte(0))))