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Joe Tsaifa02f4e2018-09-12 16:20:37 -07001// Copyright 2018 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// +build purego
6
7package impl
8
9import (
10 "fmt"
11 "reflect"
12)
13
14// offset represents the offset to a struct field, accessible from a pointer.
15// The offset is the field index into a struct.
16type offset []int
17
18// offsetOf returns a field offset for the struct field.
19func offsetOf(f reflect.StructField) offset {
20 if len(f.Index) != 1 {
21 panic("embedded structs are not supported")
22 }
23 return f.Index
24}
25
26// pointer is an abstract representation of a pointer to a struct or field.
27type pointer struct{ v reflect.Value }
28
29// pointerOfValue returns v as a pointer.
30func pointerOfValue(v reflect.Value) pointer {
31 return pointer{v: v}
32}
33
34// apply adds an offset to the pointer to derive a new pointer
35// to a specified field. The current pointer must be pointing at a struct.
36func (p pointer) apply(f offset) pointer {
37 // TODO: Handle unexported fields in an API that hides XXX fields?
38 return pointer{v: p.v.Elem().FieldByIndex(f).Addr()}
39}
40
41// asType treats p as a pointer to an object of type t and returns the value.
42func (p pointer) asType(t reflect.Type) reflect.Value {
43 if p.v.Type().Elem() != t {
44 panic(fmt.Sprintf("invalid type: got %v, want %v", p.v.Type(), t))
45 }
46 return p.v
47}