| // Copyright 2018 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. |
| |
| // +build !purego,!appengine |
| |
| package impl |
| |
| import ( |
| "reflect" |
| "unsafe" |
| ) |
| |
| // offset represents the offset to a struct field, accessible from a pointer. |
| // The offset is the byte offset to the field from the start of the struct. |
| type offset uintptr |
| |
| // offsetOf returns a field offset for the struct field. |
| func offsetOf(f reflect.StructField) offset { |
| return offset(f.Offset) |
| } |
| |
| // pointer is a pointer to a message struct or field. |
| type pointer struct{ p unsafe.Pointer } |
| |
| // pointerOfValue returns v as a pointer. |
| func pointerOfValue(v reflect.Value) pointer { |
| return pointer{p: unsafe.Pointer(v.Pointer())} |
| } |
| |
| // pointerOfIface returns the pointer portion of an interface. |
| func pointerOfIface(v interface{}) pointer { |
| type ifaceHeader struct { |
| Type unsafe.Pointer |
| Data unsafe.Pointer |
| } |
| return pointer{p: (*ifaceHeader)(unsafe.Pointer(&v)).Data} |
| } |
| |
| // IsNil reports whether the pointer is nil. |
| func (p pointer) IsNil() bool { |
| return p.p == nil |
| } |
| |
| // Apply adds an offset to the pointer to derive a new pointer |
| // to a specified field. The pointer must be valid and pointing at a struct. |
| func (p pointer) Apply(f offset) pointer { |
| if p.IsNil() { |
| panic("invalid nil pointer") |
| } |
| return pointer{p: unsafe.Pointer(uintptr(p.p) + uintptr(f))} |
| } |
| |
| // AsValueOf treats p as a pointer to an object of type t and returns the value. |
| // It is equivalent to reflect.ValueOf(p.AsIfaceOf(t)) |
| func (p pointer) AsValueOf(t reflect.Type) reflect.Value { |
| return reflect.NewAt(t, p.p) |
| } |
| |
| // AsIfaceOf treats p as a pointer to an object of type t and returns the value. |
| // It is equivalent to p.AsValueOf(t).Interface() |
| func (p pointer) AsIfaceOf(t reflect.Type) interface{} { |
| // TODO: Use tricky unsafe magic to directly create ifaceHeader. |
| return p.AsValueOf(t).Interface() |
| } |