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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.
package types
import (
// TODO(gri) Document factory, accessor methods, and fields. General clean-up.
// An Object describes a named language entity such as a package,
// constant, type, variable, function (incl. methods), or label.
// All objects implement the Object interface.
type Object interface {
Parent() *Scope // scope in which this object is declared
Pos() token.Pos // position of object identifier in declaration
Pkg() *Package // nil for objects in the Universe scope and labels
Name() string // package local object name
Type() Type // object type
Exported() bool // reports whether the name starts with a capital letter
Id() string // object id (see Id below)
// String returns a human-readable string of the object.
String() string
// order reflects a package-level object's source order: if object
// a is before object b in the source, then a.order() < b.order().
// order returns a value > 0 for package-level objects; it returns
// 0 for all other objects (including objects in file scopes).
order() uint32
// setOrder sets the order number of the object. It must be > 0.
// setParent sets the parent scope of the object.
// sameId reports whether obj.Id() and Id(pkg, name) are the same.
sameId(pkg *Package, name string) bool
// scopePos returns the start position of the scope of this Object
scopePos() token.Pos
// setScopePos sets the start position of the scope for this Object.
setScopePos(pos token.Pos)
// Id returns name if it is exported, otherwise it
// returns the name qualified with the package path.
func Id(pkg *Package, name string) string {
if ast.IsExported(name) {
return name
// unexported names need the package path for differentiation
// (if there's no package, make sure we don't start with '.'
// as that may change the order of methods between a setup
// inside a package and outside a package - which breaks some
// tests)
path := "_"
// TODO(gri): shouldn't !ast.IsExported(name) => pkg != nil be an precondition?
// if pkg == nil {
// panic("nil package in lookup of unexported name")
// }
if pkg != nil {
path = pkg.path
if path == "" {
path = "_"
return path + "." + name
// An object implements the common parts of an Object.
type object struct {
parent *Scope
pos token.Pos
pkg *Package
name string
typ Type
order_ uint32
scopePos_ token.Pos
func (obj *object) Parent() *Scope { return obj.parent }
func (obj *object) Pos() token.Pos { return obj.pos }
func (obj *object) Pkg() *Package { return obj.pkg }
func (obj *object) Name() string { return }
func (obj *object) Type() Type { return obj.typ }
func (obj *object) Exported() bool { return ast.IsExported( }
func (obj *object) Id() string { return Id(obj.pkg, }
func (obj *object) String() string { panic("abstract") }
func (obj *object) order() uint32 { return obj.order_ }
func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
func (obj *object) setParent(parent *Scope) { obj.parent = parent }
func (obj *object) setOrder(order uint32) { assert(order > 0); obj.order_ = order }
func (obj *object) setScopePos(pos token.Pos) { obj.scopePos_ = pos }
func (obj *object) sameId(pkg *Package, name string) bool {
// spec:
// "Two identifiers are different if they are spelled differently,
// or if they appear in different packages and are not exported.
// Otherwise, they are the same."
if name != {
return false
// obj.Name == name
if obj.Exported() {
return true
// not exported, so packages must be the same (pkg == nil for
// fields in Universe scope; this can only happen for types
// introduced via Eval)
if pkg == nil || obj.pkg == nil {
return pkg == obj.pkg
// pkg != nil && obj.pkg != nil
return pkg.path == obj.pkg.path
// A PkgName represents an imported Go package.
type PkgName struct {
imported *Package
used bool // set if the package was used
func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, token.NoPos}, imported, false}
// Imported returns the package that was imported.
// It is distinct from Pkg(), which is the package containing the import statement.
func (obj *PkgName) Imported() *Package { return obj.imported }
// A Const represents a declared constant.
type Const struct {
val constant.Value
visited bool // for initialization cycle detection
func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
return &Const{object{nil, pos, pkg, name, typ, 0, token.NoPos}, val, false}
func (obj *Const) Val() constant.Value { return obj.val }
// A TypeName represents a declared type.
type TypeName struct {
func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
return &TypeName{object{nil, pos, pkg, name, typ, 0, token.NoPos}}
// A Variable represents a declared variable (including function parameters and results, and struct fields).
type Var struct {
anonymous bool // if set, the variable is an anonymous struct field, and name is the type name
visited bool // for initialization cycle detection
isField bool // var is struct field
used bool // set if the variable was used
func NewVar(pos token.Pos, pkg *Package, name string, typ Type) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}}
func NewParam(pos token.Pos, pkg *Package, name string, typ Type) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}, used: true} // parameters are always 'used'
func NewField(pos token.Pos, pkg *Package, name string, typ Type, anonymous bool) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}, anonymous: anonymous, isField: true}
func (obj *Var) Anonymous() bool { return obj.anonymous }
func (obj *Var) IsField() bool { return obj.isField }
// A Func represents a declared function, concrete method, or abstract
// (interface) method. Its Type() is always a *Signature.
// An abstract method may belong to many interfaces due to embedding.
type Func struct {
func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
// don't store a nil signature
var typ Type
if sig != nil {
typ = sig
return &Func{object{nil, pos, pkg, name, typ, 0, token.NoPos}}
// FullName returns the package- or receiver-type-qualified name of
// function or method obj.
func (obj *Func) FullName() string {
var buf bytes.Buffer
writeFuncName(&buf, obj, nil)
return buf.String()
func (obj *Func) Scope() *Scope {
return obj.typ.(*Signature).scope
// A Label represents a declared label.
type Label struct {
used bool // set if the label was used
func NewLabel(pos token.Pos, pkg *Package, name string) *Label {
return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid]}, false}
// A Builtin represents a built-in function.
// Builtins don't have a valid type.
type Builtin struct {
id builtinId
func newBuiltin(id builtinId) *Builtin {
return &Builtin{object{name: predeclaredFuncs[id].name, typ: Typ[Invalid]}, id}
// Nil represents the predeclared value nil.
type Nil struct {
func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
typ := obj.Type()
switch obj := obj.(type) {
case *PkgName:
fmt.Fprintf(buf, "package %s", obj.Name())
if path := obj.imported.path; path != "" && path != {
fmt.Fprintf(buf, " (%q)", path)
case *Const:
case *TypeName:
typ = typ.Underlying()
case *Var:
if obj.isField {
} else {
case *Func:
buf.WriteString("func ")
writeFuncName(buf, obj, qf)
if typ != nil {
WriteSignature(buf, typ.(*Signature), qf)
case *Label:
typ = nil
case *Builtin:
typ = nil
case *Nil:
panic(fmt.Sprintf("writeObject(%T)", obj))
buf.WriteByte(' ')
// For package-level objects, qualify the name.
if obj.Pkg() != nil && obj.Pkg().scope.Lookup(obj.Name()) == obj {
writePackage(buf, obj.Pkg(), qf)
if typ != nil {
buf.WriteByte(' ')
WriteType(buf, typ, qf)
func writePackage(buf *bytes.Buffer, pkg *Package, qf Qualifier) {
if pkg == nil {
var s string
if qf != nil {
s = qf(pkg)
} else {
s = pkg.Path()
if s != "" {
// ObjectString returns the string form of obj.
// The Qualifier controls the printing of
// package-level objects, and may be nil.
func ObjectString(obj Object, qf Qualifier) string {
var buf bytes.Buffer
writeObject(&buf, obj, qf)
return buf.String()
func (obj *PkgName) String() string { return ObjectString(obj, nil) }
func (obj *Const) String() string { return ObjectString(obj, nil) }
func (obj *TypeName) String() string { return ObjectString(obj, nil) }
func (obj *Var) String() string { return ObjectString(obj, nil) }
func (obj *Func) String() string { return ObjectString(obj, nil) }
func (obj *Label) String() string { return ObjectString(obj, nil) }
func (obj *Builtin) String() string { return ObjectString(obj, nil) }
func (obj *Nil) String() string { return ObjectString(obj, nil) }
func writeFuncName(buf *bytes.Buffer, f *Func, qf Qualifier) {
if f.typ != nil {
sig := f.typ.(*Signature)
if recv := sig.Recv(); recv != nil {
if _, ok := recv.Type().(*Interface); ok {
// gcimporter creates abstract methods of
// named interfaces using the interface type
// (not the named type) as the receiver.
// Don't print it in full.
} else {
WriteType(buf, recv.Type(), qf)
} else if f.pkg != nil {
writePackage(buf, f.pkg, qf)