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Source file src/go/types/object.go

Documentation: go/types

  // 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; nil for methods and struct fields
  	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 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
  	// 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 := "_"
  	// 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
  	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 obj.name }
  func (obj *object) Type() Type          { return obj.typ }
  func (obj *object) Exported() bool      { return ast.IsExported(obj.name) }
  func (obj *object) Id() string          { return Id(obj.pkg, obj.name) }
  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 != obj.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 }
  func (*Const) isDependency()           {} // a constant may be a dependency of an initialization expression
  // A TypeName represents a name for a (named or alias) 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}}
  // 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.name != obj.name || 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 {
  	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 }
  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 {
  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 }
  func (*Func) isDependency()     {} // a function may be a dependency of an initialization expression
  // 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) {
  	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 != obj.name {
  			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 tname.IsAlias() {
  			buf.WriteString(" =")
  		} else {
  			typ = typ.Underlying()
  	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)

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