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Source file src/go/types/type.go

Documentation: go/types

  // Copyright 2011 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 "sort"
  // A Type represents a type of Go.
  // All types implement the Type interface.
  type Type interface {
  	// Underlying returns the underlying type of a type.
  	Underlying() Type
  	// String returns a string representation of a type.
  	String() string
  // BasicKind describes the kind of basic type.
  type BasicKind int
  const (
  	Invalid BasicKind = iota // type is invalid
  	// predeclared types
  	// types for untyped values
  	// aliases
  	Byte = Uint8
  	Rune = Int32
  // BasicInfo is a set of flags describing properties of a basic type.
  type BasicInfo int
  // Properties of basic types.
  const (
  	IsBoolean BasicInfo = 1 << iota
  	IsOrdered   = IsInteger | IsFloat | IsString
  	IsNumeric   = IsInteger | IsFloat | IsComplex
  	IsConstType = IsBoolean | IsNumeric | IsString
  // A Basic represents a basic type.
  type Basic struct {
  	kind BasicKind
  	info BasicInfo
  	name string
  // Kind returns the kind of basic type b.
  func (b *Basic) Kind() BasicKind { return b.kind }
  // Info returns information about properties of basic type b.
  func (b *Basic) Info() BasicInfo { return b.info }
  // Name returns the name of basic type b.
  func (b *Basic) Name() string { return b.name }
  // An Array represents an array type.
  type Array struct {
  	len  int64
  	elem Type
  // NewArray returns a new array type for the given element type and length.
  func NewArray(elem Type, len int64) *Array { return &Array{len, elem} }
  // Len returns the length of array a.
  func (a *Array) Len() int64 { return a.len }
  // Elem returns element type of array a.
  func (a *Array) Elem() Type { return a.elem }
  // A Slice represents a slice type.
  type Slice struct {
  	elem Type
  // NewSlice returns a new slice type for the given element type.
  func NewSlice(elem Type) *Slice { return &Slice{elem} }
  // Elem returns the element type of slice s.
  func (s *Slice) Elem() Type { return s.elem }
  // A Struct represents a struct type.
  type Struct struct {
  	fields []*Var
  	tags   []string // field tags; nil if there are no tags
  // NewStruct returns a new struct with the given fields and corresponding field tags.
  // If a field with index i has a tag, tags[i] must be that tag, but len(tags) may be
  // only as long as required to hold the tag with the largest index i. Consequently,
  // if no field has a tag, tags may be nil.
  func NewStruct(fields []*Var, tags []string) *Struct {
  	var fset objset
  	for _, f := range fields {
  		if f.name != "_" && fset.insert(f) != nil {
  			panic("multiple fields with the same name")
  	if len(tags) > len(fields) {
  		panic("more tags than fields")
  	return &Struct{fields: fields, tags: tags}
  // NumFields returns the number of fields in the struct (including blank and anonymous fields).
  func (s *Struct) NumFields() int { return len(s.fields) }
  // Field returns the i'th field for 0 <= i < NumFields().
  func (s *Struct) Field(i int) *Var { return s.fields[i] }
  // Tag returns the i'th field tag for 0 <= i < NumFields().
  func (s *Struct) Tag(i int) string {
  	if i < len(s.tags) {
  		return s.tags[i]
  	return ""
  // A Pointer represents a pointer type.
  type Pointer struct {
  	base Type // element type
  // NewPointer returns a new pointer type for the given element (base) type.
  func NewPointer(elem Type) *Pointer { return &Pointer{base: elem} }
  // Elem returns the element type for the given pointer p.
  func (p *Pointer) Elem() Type { return p.base }
  // A Tuple represents an ordered list of variables; a nil *Tuple is a valid (empty) tuple.
  // Tuples are used as components of signatures and to represent the type of multiple
  // assignments; they are not first class types of Go.
  type Tuple struct {
  	vars []*Var
  // NewTuple returns a new tuple for the given variables.
  func NewTuple(x ...*Var) *Tuple {
  	if len(x) > 0 {
  		return &Tuple{x}
  	return nil
  // Len returns the number variables of tuple t.
  func (t *Tuple) Len() int {
  	if t != nil {
  		return len(t.vars)
  	return 0
  // At returns the i'th variable of tuple t.
  func (t *Tuple) At(i int) *Var { return t.vars[i] }
  // A Signature represents a (non-builtin) function or method type.
  type Signature struct {
  	// We need to keep the scope in Signature (rather than passing it around
  	// and store it in the Func Object) because when type-checking a function
  	// literal we call the general type checker which returns a general Type.
  	// We then unpack the *Signature and use the scope for the literal body.
  	scope    *Scope // function scope, present for package-local signatures
  	recv     *Var   // nil if not a method
  	params   *Tuple // (incoming) parameters from left to right; or nil
  	results  *Tuple // (outgoing) results from left to right; or nil
  	variadic bool   // true if the last parameter's type is of the form ...T (or string, for append built-in only)
  // NewSignature returns a new function type for the given receiver, parameters,
  // and results, either of which may be nil. If variadic is set, the function
  // is variadic, it must have at least one parameter, and the last parameter
  // must be of unnamed slice type.
  func NewSignature(recv *Var, params, results *Tuple, variadic bool) *Signature {
  	if variadic {
  		n := params.Len()
  		if n == 0 {
  			panic("types.NewSignature: variadic function must have at least one parameter")
  		if _, ok := params.At(n - 1).typ.(*Slice); !ok {
  			panic("types.NewSignature: variadic parameter must be of unnamed slice type")
  	return &Signature{nil, recv, params, results, variadic}
  // Recv returns the receiver of signature s (if a method), or nil if a
  // function.
  // For an abstract method, Recv returns the enclosing interface either
  // as a *Named or an *Interface. Due to embedding, an interface may
  // contain methods whose receiver type is a different interface.
  func (s *Signature) Recv() *Var { return s.recv }
  // Params returns the parameters of signature s, or nil.
  func (s *Signature) Params() *Tuple { return s.params }
  // Results returns the results of signature s, or nil.
  func (s *Signature) Results() *Tuple { return s.results }
  // Variadic reports whether the signature s is variadic.
  func (s *Signature) Variadic() bool { return s.variadic }
  // An Interface represents an interface type.
  type Interface struct {
  	methods   []*Func  // ordered list of explicitly declared methods
  	embeddeds []*Named // ordered list of explicitly embedded types
  	allMethods []*Func // ordered list of methods declared with or embedded in this interface (TODO(gri): replace with mset)
  // NewInterface returns a new interface for the given methods and embedded types.
  func NewInterface(methods []*Func, embeddeds []*Named) *Interface {
  	typ := new(Interface)
  	var mset objset
  	for _, m := range methods {
  		if mset.insert(m) != nil {
  			panic("multiple methods with the same name")
  		// set receiver
  		// TODO(gri) Ideally, we should use a named type here instead of
  		// typ, for less verbose printing of interface method signatures.
  		m.typ.(*Signature).recv = NewVar(m.pos, m.pkg, "", typ)
  	if embeddeds == nil {
  	typ.methods = methods
  	typ.embeddeds = embeddeds
  	return typ
  // NumExplicitMethods returns the number of explicitly declared methods of interface t.
  func (t *Interface) NumExplicitMethods() int { return len(t.methods) }
  // ExplicitMethod returns the i'th explicitly declared method of interface t for 0 <= i < t.NumExplicitMethods().
  // The methods are ordered by their unique Id.
  func (t *Interface) ExplicitMethod(i int) *Func { return t.methods[i] }
  // NumEmbeddeds returns the number of embedded types in interface t.
  func (t *Interface) NumEmbeddeds() int { return len(t.embeddeds) }
  // Embedded returns the i'th embedded type of interface t for 0 <= i < t.NumEmbeddeds().
  // The types are ordered by the corresponding TypeName's unique Id.
  func (t *Interface) Embedded(i int) *Named { return t.embeddeds[i] }
  // NumMethods returns the total number of methods of interface t.
  func (t *Interface) NumMethods() int { return len(t.allMethods) }
  // Method returns the i'th method of interface t for 0 <= i < t.NumMethods().
  // The methods are ordered by their unique Id.
  func (t *Interface) Method(i int) *Func { return t.allMethods[i] }
  // Empty returns true if t is the empty interface.
  func (t *Interface) Empty() bool { return len(t.allMethods) == 0 }
  // Complete computes the interface's method set. It must be called by users of
  // NewInterface after the interface's embedded types are fully defined and
  // before using the interface type in any way other than to form other types.
  // Complete returns the receiver.
  func (t *Interface) Complete() *Interface {
  	if t.allMethods != nil {
  		return t
  	var allMethods []*Func
  	if t.embeddeds == nil {
  		if t.methods == nil {
  			allMethods = make([]*Func, 0, 1)
  		} else {
  			allMethods = t.methods
  	} else {
  		allMethods = append(allMethods, t.methods...)
  		for _, et := range t.embeddeds {
  			it := et.Underlying().(*Interface)
  			for _, tm := range it.allMethods {
  				// Make a copy of the method and adjust its receiver type.
  				newm := *tm
  				newmtyp := *tm.typ.(*Signature)
  				newm.typ = &newmtyp
  				newmtyp.recv = NewVar(newm.pos, newm.pkg, "", t)
  				allMethods = append(allMethods, &newm)
  	t.allMethods = allMethods
  	return t
  // A Map represents a map type.
  type Map struct {
  	key, elem Type
  // NewMap returns a new map for the given key and element types.
  func NewMap(key, elem Type) *Map {
  	return &Map{key, elem}
  // Key returns the key type of map m.
  func (m *Map) Key() Type { return m.key }
  // Elem returns the element type of map m.
  func (m *Map) Elem() Type { return m.elem }
  // A Chan represents a channel type.
  type Chan struct {
  	dir  ChanDir
  	elem Type
  // A ChanDir value indicates a channel direction.
  type ChanDir int
  // The direction of a channel is indicated by one of these constants.
  const (
  	SendRecv ChanDir = iota
  // NewChan returns a new channel type for the given direction and element type.
  func NewChan(dir ChanDir, elem Type) *Chan {
  	return &Chan{dir, elem}
  // Dir returns the direction of channel c.
  func (c *Chan) Dir() ChanDir { return c.dir }
  // Elem returns the element type of channel c.
  func (c *Chan) Elem() Type { return c.elem }
  // A Named represents a named type.
  type Named struct {
  	obj        *TypeName // corresponding declared object
  	underlying Type      // possibly a *Named during setup; never a *Named once set up completely
  	methods    []*Func   // methods declared for this type (not the method set of this type)
  // NewNamed returns a new named type for the given type name, underlying type, and associated methods.
  // The underlying type must not be a *Named.
  func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
  	if _, ok := underlying.(*Named); ok {
  		panic("types.NewNamed: underlying type must not be *Named")
  	typ := &Named{obj: obj, underlying: underlying, methods: methods}
  	if obj.typ == nil {
  		obj.typ = typ
  	return typ
  // Obj returns the type name for the named type t.
  func (t *Named) Obj() *TypeName { return t.obj }
  // NumMethods returns the number of explicit methods whose receiver is named type t.
  func (t *Named) NumMethods() int { return len(t.methods) }
  // Method returns the i'th method of named type t for 0 <= i < t.NumMethods().
  func (t *Named) Method(i int) *Func { return t.methods[i] }
  // SetUnderlying sets the underlying type and marks t as complete.
  // TODO(gri) determine if there's a better solution rather than providing this function
  func (t *Named) SetUnderlying(underlying Type) {
  	if underlying == nil {
  		panic("types.Named.SetUnderlying: underlying type must not be nil")
  	if _, ok := underlying.(*Named); ok {
  		panic("types.Named.SetUnderlying: underlying type must not be *Named")
  	t.underlying = underlying
  // AddMethod adds method m unless it is already in the method list.
  // TODO(gri) find a better solution instead of providing this function
  func (t *Named) AddMethod(m *Func) {
  	if i, _ := lookupMethod(t.methods, m.pkg, m.name); i < 0 {
  		t.methods = append(t.methods, m)
  // Implementations for Type methods.
  func (t *Basic) Underlying() Type     { return t }
  func (t *Array) Underlying() Type     { return t }
  func (t *Slice) Underlying() Type     { return t }
  func (t *Struct) Underlying() Type    { return t }
  func (t *Pointer) Underlying() Type   { return t }
  func (t *Tuple) Underlying() Type     { return t }
  func (t *Signature) Underlying() Type { return t }
  func (t *Interface) Underlying() Type { return t }
  func (t *Map) Underlying() Type       { return t }
  func (t *Chan) Underlying() Type      { return t }
  func (t *Named) Underlying() Type     { return t.underlying }
  func (t *Basic) String() string     { return TypeString(t, nil) }
  func (t *Array) String() string     { return TypeString(t, nil) }
  func (t *Slice) String() string     { return TypeString(t, nil) }
  func (t *Struct) String() string    { return TypeString(t, nil) }
  func (t *Pointer) String() string   { return TypeString(t, nil) }
  func (t *Tuple) String() string     { return TypeString(t, nil) }
  func (t *Signature) String() string { return TypeString(t, nil) }
  func (t *Interface) String() string { return TypeString(t, nil) }
  func (t *Map) String() string       { return TypeString(t, nil) }
  func (t *Chan) String() string      { return TypeString(t, nil) }
  func (t *Named) String() string     { return TypeString(t, nil) }

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