patch reflect: Zero/Len

Author: xushiwei

_demo/rtype/rtype.go

@@ -5,4 +5,7 @@ import "reflect"
 func main() {
 	tyIntSlice := reflect.SliceOf(reflect.TypeOf(0))
 	println(tyIntSlice.String())
+
+	v := reflect.Zero(tyIntSlice)
+	println(v.Len())
 }

internal/abi/type.go

@@ -329,6 +329,22 @@ func (p *Imethod) PkgPath() string {
 
 func (t *Type) Kind() Kind { return Kind(t.Kind_ & KindMask) }
 
+func (t *Type) HasName() bool {
+	return t.TFlag&TFlagNamed != 0
+}
+
+func (t *Type) Pointers() bool { return t.PtrBytes != 0 }
+
+// IfaceIndir reports whether t is stored indirectly in an interface value.
+func (t *Type) IfaceIndir() bool {
+	return t.Kind_&KindDirectIface == 0
+}
+
+// isDirectIface reports whether t is stored directly in an interface value.
+func (t *Type) IsDirectIface() bool {
+	return t.Kind_&KindDirectIface != 0
+}
+
 // Size returns the size of data with type t.
 func (t *Type) Size() uintptr { return t.Size_ }
 
@@ -340,7 +356,7 @@ func (t *Type) FieldAlign() int { return int(t.FieldAlign_) }
 // String returns string form of type t.
 func (t *Type) String() string {
 	if t.TFlag&TFlagExtraStar != 0 {
-		return "*" + t.Str_
+		return "*" + t.Str_ // TODO(xsw): misunderstand
 	}
 	return t.Str_
 }

internal/lib/reflect/unsafeheader.go

@@ -0,0 +1,37 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package unsafeheader contains header declarations for the Go runtime's slice
+// and string implementations.
+//
+// This package allows packages that cannot import "reflect" to use types that
+// are tested to be equivalent to reflect.SliceHeader and reflect.StringHeader.
+package reflect
+
+import (
+	"unsafe"
+)
+
+// unsafeheaderSlice is the runtime representation of a slice.
+// It cannot be used safely or portably and its representation may
+// change in a later release.
+//
+// Unlike reflect.SliceHeader, its Data field is sufficient to guarantee the
+// data it references will not be garbage collected.
+type unsafeheaderSlice struct {
+	Data unsafe.Pointer
+	Len  int
+	Cap  int
+}
+
+// unsafeheaderString is the runtime representation of a string.
+// It cannot be used safely or portably and its representation may
+// change in a later release.
+//
+// Unlike reflect.StringHeader, its Data field is sufficient to guarantee the
+// data it references will not be garbage collected.
+type unsafeheaderString struct {
+	Data unsafe.Pointer
+	Len  int
+}