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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 (
// 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; nil for methods and struct fields
Pos() token.Pos // position of object identifier in declaration
Pkg() *Package // package to which this object belongs; nil for labels and objects in the Universe scope
Name() string // package local object name
Type() Type // object type
Exported() bool // reports whether the name starts with a capital letter
Id() string // object name if exported, qualified name if not exported (see func Id)
// 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
// color returns the object's color.
color() color
// setType sets the type of the object.
// setOrder sets the order number of the object. It must be > 0.
// setColor sets the object's color. It must not be white.
setColor(color color)
// 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 token.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 := "_"
// pkg is nil for objects in Universe scope and possibly types
// introduced via Eval (see also comment in object.sameId)
if pkg != nil && pkg.path != "" {
path = pkg.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
color_ color
scopePos_ token.Pos
// color encodes the color of an object (see Checker.objDecl for details).
type color uint32
// An object may be painted in one of three colors.
// Color values other than white or black are considered grey.
const (
white color = iota
grey // must be > white and black
func (c color) String() string {
switch c {
case white:
return "white"
case black:
return "black"
return "grey"
// colorFor returns the (initial) color for an object depending on
// whether its type t is known or not.
func colorFor(t Type) color {
if t != nil {
return black
return white
// Parent returns the scope in which the object is declared.
// The result is nil for methods and struct fields.
func (obj *object) Parent() *Scope { return obj.parent }
// Pos returns the declaration position of the object's identifier.
func (obj *object) Pos() token.Pos { return obj.pos }
// Pkg returns the package to which the object belongs.
// The result is nil for labels and objects in the Universe scope.
func (obj *object) Pkg() *Package { return obj.pkg }
// Name returns the object's (package-local, unqualified) name.
func (obj *object) Name() string { return }
// Type returns the object's type.
func (obj *object) Type() Type { return obj.typ }
// Exported reports whether the object is exported (starts with a capital letter).
// It doesn't take into account whether the object is in a local (function) scope
// or not.
func (obj *object) Exported() bool { return token.IsExported( }
// Id is a wrapper for Id(obj.Pkg(), obj.Name()).
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) color() color { return obj.color_ }
func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
func (obj *object) setParent(parent *Scope) { obj.parent = parent }
func (obj *object) setType(typ Type) { obj.typ = typ }
func (obj *object) setOrder(order uint32) { assert(order > 0); obj.order_ = order }
func (obj *object) setColor(color color) { assert(color != white); obj.color_ = color }
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.
// PkgNames don't have a type.
type PkgName struct {
imported *Package
used bool // set if the package was used
// NewPkgName returns a new PkgName object representing an imported package.
// The remaining arguments set the attributes found with all Objects.
func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, 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
// NewConst returns a new constant with value val.
// The remaining arguments set the attributes found with all Objects.
func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
return &Const{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, val}
// Val returns the constant's value.
func (obj *Const) Val() constant.Value { return obj.val }
func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
// A TypeName represents a name for a (defined or alias) type.
type TypeName struct {
// NewTypeName returns a new type name denoting the given typ.
// The remaining arguments set the attributes found with all Objects.
// The typ argument may be a defined (Named) type or an alias type.
// It may also be nil such that the returned TypeName can be used as
// argument for NewNamed, which will set the TypeName's type as a side-
// effect.
func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
return &TypeName{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
// _NewTypeNameLazy returns a new defined type like NewTypeName, but it
// lazily calls resolve to finish constructing the Named object.
func _NewTypeNameLazy(pos token.Pos, pkg *Package, name string, load func(named *Named) (tparams []*TypeParam, underlying Type, methods []*Func)) *TypeName {
obj := NewTypeName(pos, pkg, name, nil)
resolve := func(_ *Context, t *Named) (*TypeParamList, Type, []*Func) {
tparams, underlying, methods := load(t)
switch underlying.(type) {
case nil, *Named:
panic(fmt.Sprintf("invalid underlying type %T", t.underlying))
return bindTParams(tparams), underlying, methods
NewNamed(obj, nil, nil).resolver = resolve
return obj
// IsAlias reports whether obj is an alias name for a type.
func (obj *TypeName) IsAlias() bool {
switch t := obj.typ.(type) {
case nil:
return false
case *Basic:
// unsafe.Pointer is not an alias.
if obj.pkg == Unsafe {
return false
// Any user-defined type name for a basic type is an alias for a
// basic type (because basic types are pre-declared in the Universe
// scope, outside any package scope), and so is any type name with
// a different name than the name of the basic type it refers to.
// Additionally, we need to look for "byte" and "rune" because they
// are aliases but have the same names (for better error messages).
return obj.pkg != nil || != || t == universeByte || t == universeRune
case *Named:
return obj != t.obj
return true
// A Variable represents a declared variable (including function parameters and results, and struct fields).
type Var struct {
embedded bool // if set, the variable is an embedded struct field, and name is the type name
isField bool // var is struct field
used bool // set if the variable was used
// NewVar returns a new variable.
// The arguments set the attributes found with all Objects.
func NewVar(pos token.Pos, pkg *Package, name string, typ Type) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
// NewParam returns a new variable representing a function parameter.
func NewParam(pos token.Pos, pkg *Package, name string, typ Type) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, used: true} // parameters are always 'used'
// NewField returns a new variable representing a struct field.
// For embedded fields, the name is the unqualified type name
/// under which the field is accessible.
func NewField(pos token.Pos, pkg *Package, name string, typ Type, embedded bool) *Var {
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, embedded: embedded, isField: true}
// Anonymous reports whether the variable is an embedded field.
// Same as Embedded; only present for backward-compatibility.
func (obj *Var) Anonymous() bool { return obj.embedded }
// Embedded reports whether the variable is an embedded field.
func (obj *Var) Embedded() bool { return obj.embedded }
// IsField reports whether the variable is a struct field.
func (obj *Var) IsField() bool { return obj.isField }
func (*Var) isDependency() {} // a variable may be a dependency of an initialization expression
// 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 {
instRecv *Named // if non-nil, the receiver type for an incomplete instance method
hasPtrRecv_ bool // only valid for methods that don't have a type yet; use hasPtrRecv() to read
// NewFunc returns a new function with the given signature, representing
// the function's type.
func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
// don't store a (typed) nil signature
var typ Type
if sig != nil {
typ = sig
return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, nil, false}
// 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()
// Scope returns the scope of the function's body block.
func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
// hasPtrRecv reports whether the receiver is of the form *T for the given method obj.
func (obj *Func) hasPtrRecv() bool {
// If a method's receiver type is set, use that as the source of truth for the receiver.
// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
// signature. We may reach here before the signature is fully set up: we must explicitly
// check if the receiver is set (we cannot just look for non-nil obj.typ).
if sig, _ := obj.typ.(*Signature); sig != nil && sig.recv != nil {
_, isPtr := deref(sig.recv.typ)
return isPtr
// If a method's type is not set it may be a method/function that is:
// 1) client-supplied (via NewFunc with no signature), or
// 2) internally created but not yet type-checked.
// For case 1) we can't do anything; the client must know what they are doing.
// For case 2) we can use the information gathered by the resolver.
return obj.hasPtrRecv_
func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
// A Label represents a declared label.
// Labels don't have a type.
type Label struct {
used bool // set if the label was used
// NewLabel returns a new label.
func NewLabel(pos token.Pos, pkg *Package, name string) *Label {
return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid], color_: black}, 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], color_: black}, id}
// Nil represents the predeclared value nil.
type Nil struct {
func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
var tname *TypeName
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:
tname = obj
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 {
if tname != nil {
// We have a type object: Don't print anything more for
// basic types since there's no more information (names
// are the same; see also comment in TypeName.IsAlias).
if _, ok := typ.(*Basic); ok {
if named, _ := typ.(*Named); named != nil && named.TypeParams().Len() > 0 {
newTypeWriter(buf, qf).tParamList(named.TypeParams().list())
if tname.IsAlias() {
buf.WriteString(" =")
} else {
typ = under(typ)
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)