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// Copyright 2013 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.
// This file implements Selections.
package types
import (
// SelectionKind describes the kind of a selector expression x.f
// (excluding qualified identifiers).
type SelectionKind int
const (
FieldVal SelectionKind = iota // x.f is a struct field selector
MethodVal // x.f is a method selector
MethodExpr // x.f is a method expression
// A Selection describes a selector expression x.f.
// For the declarations:
// type T struct{ x int; E }
// type E struct{}
// func (e E) m() {}
// var p *T
// the following relations exist:
// Selector Kind Recv Obj Type Index Indirect
// p.x FieldVal T x int {0} true
// p.m MethodVal *T m func (e *T) m() {1, 0} true
// T.m MethodExpr T m func m(_ T) {1, 0} false
type Selection struct {
kind SelectionKind
recv Type // type of x
obj Object // object denoted by x.f
index []int // path from x to x.f
indirect bool // set if there was any pointer indirection on the path
// Kind returns the selection kind.
func (s *Selection) Kind() SelectionKind { return s.kind }
// Recv returns the type of x in x.f.
func (s *Selection) Recv() Type { return s.recv }
// Obj returns the object denoted by x.f; a *Var for
// a field selection, and a *Func in all other cases.
func (s *Selection) Obj() Object { return s.obj }
// Type returns the type of x.f, which may be different from the type of f.
// See Selection for more information.
func (s *Selection) Type() Type {
switch s.kind {
case MethodVal:
// The type of x.f is a method with its receiver type set
// to the type of x.
sig := *s.obj.(*Func).typ.(*Signature)
recv := *sig.recv
recv.typ = s.recv
sig.recv = &recv
return &sig
case MethodExpr:
// The type of x.f is a function (without receiver)
// and an additional first argument with the same type as x.
// TODO(gri) Similar code is already in call.go - factor!
// TODO(gri) Compute this eagerly to avoid allocations.
sig := *s.obj.(*Func).typ.(*Signature)
arg0 := *sig.recv
sig.recv = nil
arg0.typ = s.recv
var params []*Var
if sig.params != nil {
params = sig.params.vars
sig.params = NewTuple(append([]*Var{&arg0}, params...)...)
return &sig
// In all other cases, the type of x.f is the type of x.
return s.obj.Type()
// Index describes the path from x to f in x.f.
// The last index entry is the field or method index of the type declaring f;
// either:
// 1) the list of declared methods of a named type; or
// 2) the list of methods of an interface type; or
// 3) the list of fields of a struct type.
// The earlier index entries are the indices of the embedded fields implicitly
// traversed to get from (the type of) x to f, starting at embedding depth 0.
func (s *Selection) Index() []int { return s.index }
// Indirect reports whether any pointer indirection was required to get from
// x to f in x.f.
func (s *Selection) Indirect() bool { return s.indirect }
func (s *Selection) String() string { return SelectionString(s, nil) }
// SelectionString returns the string form of s.
// The Qualifier controls the printing of
// package-level objects, and may be nil.
// Examples:
// "field (T) f int"
// "method (T) f(X) Y"
// "method expr (T) f(X) Y"
func SelectionString(s *Selection, qf Qualifier) string {
var k string
switch s.kind {
case FieldVal:
k = "field "
case MethodVal:
k = "method "
case MethodExpr:
k = "method expr "
var buf bytes.Buffer
WriteType(&buf, s.Recv(), qf)
fmt.Fprintf(&buf, ") %s", s.obj.Name())
if T := s.Type(); s.kind == FieldVal {
buf.WriteByte(' ')
WriteType(&buf, T, qf)
} else {
WriteSignature(&buf, T.(*Signature), qf)
return buf.String()