blob: d27f8cfd4d69da42235719203fa62496fc2a706e [file] [log] [blame]
// Copyright 2021 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 (
// ----------------------------------------------------------------------------
// API
// An Interface represents an interface type.
type Interface struct {
obj *TypeName // type name object defining this interface; or nil (for better error messages)
methods []*Func // ordered list of explicitly declared methods
embeddeds []Type // ordered list of explicitly embedded elements
embedPos *[]token.Pos // positions of embedded elements; or nil (for error messages) - use pointer to save space
complete bool // indicates that obj, methods, and embeddeds are set and type set can be computed
tset *_TypeSet // type set described by this interface, computed lazily
// typeSet returns the type set for interface t.
func (t *Interface) typeSet() *_TypeSet { return computeInterfaceTypeSet(nil, token.NoPos, t) }
// emptyInterface represents the empty (completed) interface
var emptyInterface = Interface{complete: true, tset: &topTypeSet}
// NewInterface returns a new interface for the given methods and embedded types.
// NewInterface takes ownership of the provided methods and may modify their types
// by setting missing receivers.
// Deprecated: Use NewInterfaceType instead which allows arbitrary embedded types.
func NewInterface(methods []*Func, embeddeds []*Named) *Interface {
tnames := make([]Type, len(embeddeds))
for i, t := range embeddeds {
tnames[i] = t
return NewInterfaceType(methods, tnames)
// NewInterfaceType returns a new interface for the given methods and embedded
// types. NewInterfaceType takes ownership of the provided methods and may
// modify their types by setting missing receivers.
// To avoid race conditions, the interface's type set should be computed before
// concurrent use of the interface, by explicitly calling Complete.
func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
if len(methods) == 0 && len(embeddeds) == 0 {
return &emptyInterface
// set method receivers if necessary
typ := new(Interface)
for _, m := range methods {
if sig := m.typ.(*Signature); sig.recv == nil {
sig.recv = NewVar(m.pos, m.pkg, "", typ)
// sort for API stability
typ.methods = methods
typ.embeddeds = embeddeds
typ.complete = true
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 defined (*Named) type of interface t for 0 <= i < t.NumEmbeddeds().
// The result is nil if the i'th embedded type is not a defined type.
// Deprecated: Use EmbeddedType which is not restricted to defined (*Named) types.
func (t *Interface) Embedded(i int) *Named { tname, _ := t.embeddeds[i].(*Named); return tname }
// EmbeddedType returns the i'th embedded type of interface t for 0 <= i < t.NumEmbeddeds().
func (t *Interface) EmbeddedType(i int) Type { return t.embeddeds[i] }
// NumMethods returns the total number of methods of interface t.
func (t *Interface) NumMethods() int { return t.typeSet().NumMethods() }
// 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.typeSet().Method(i) }
// Empty reports whether t is the empty interface.
func (t *Interface) Empty() bool { return t.typeSet().IsAll() }
// IsComparable reports whether each type in interface t's type set is comparable.
func (t *Interface) IsComparable() bool { return t.typeSet().IsComparable() }
// IsConstraint reports whether interface t is not just a method set.
func (t *Interface) IsConstraint() bool { return !t.typeSet().IsMethodSet() }
// Complete computes the interface's type set. It must be called by users of
// NewInterfaceType and 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. The interface must not contain duplicate methods or a
// panic occurs. Complete returns the receiver.
// Interface types that have been completed are safe for concurrent use.
func (t *Interface) Complete() *Interface {
if !t.complete {
t.complete = true
t.typeSet() // checks if t.tset is already set
return t
func (t *Interface) Underlying() Type { return t }
func (t *Interface) String() string { return TypeString(t, nil) }
// ----------------------------------------------------------------------------
// Implementation
func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, def *Named) {
var tlist []ast.Expr
var tname *ast.Ident // "type" name of first entry in a type list declaration
addEmbedded := func(pos token.Pos, typ Type) {
ityp.embeddeds = append(ityp.embeddeds, typ)
if ityp.embedPos == nil {
ityp.embedPos = new([]token.Pos)
*ityp.embedPos = append(*ityp.embedPos, pos)
for _, f := range iface.Methods.List {
if len(f.Names) == 0 {
// We have an embedded type; possibly a union of types.
addEmbedded(f.Type.Pos(), parseUnion(check, flattenUnion(nil, f.Type)))
// We have a method with name f.Names[0], or a type
// of a type list (name.Name == "type").
// (The parser ensures that there's only one method
// and we don't care if a constructed AST has more.)
name := f.Names[0]
if name.Name == "_" {
check.errorf(name, _BlankIfaceMethod, "invalid method name _")
continue // ignore
// TODO(rfindley) Remove type list handling once the parser doesn't accept type lists anymore.
if name.Name == "type" {
// Report an error for the first type list per interface
// if we don't allow type lists, but continue.
if !allowTypeLists && tlist == nil {
check.softErrorf(name, _Todo, "use generalized embedding syntax instead of a type list")
// For now, collect all type list entries as if it
// were a single union, where each union element is
// of the form ~T.
// TODO(rfindley) remove once we disallow type lists
op := new(ast.UnaryExpr)
op.Op = token.TILDE
op.X = f.Type
tlist = append(tlist, op)
// Report an error if we have multiple type lists in an
// interface, but only if they are permitted in the first place.
if allowTypeLists && tname != nil && tname != name {
check.errorf(name, _Todo, "cannot have multiple type lists in an interface")
tname = name
typ := check.typ(f.Type)
sig, _ := typ.(*Signature)
if sig == nil {
if typ != Typ[Invalid] {
check.invalidAST(f.Type, "%s is not a method signature", typ)
continue // ignore
// Always type-check method type parameters but complain if they are not enabled.
// (This extra check is needed here because interface method signatures don't have
// a receiver specification.)
if sig.tparams != nil {
var at positioner = f.Type
if tparams := typeparams.Get(f.Type); tparams != nil {
at = tparams
check.errorf(at, _Todo, "methods cannot have type parameters")
// use named receiver type if available (for better error messages)
var recvTyp Type = ityp
if def != nil {
recvTyp = def
sig.recv = NewVar(name.Pos(), check.pkg, "", recvTyp)
m := NewFunc(name.Pos(), check.pkg, name.Name, sig)
check.recordDef(name, m)
ityp.methods = append(ityp.methods, m)
// type constraints
if tlist != nil {
// TODO(rfindley): this differs from types2 due to the use of Pos() below,
// which should actually be on the ~. Confirm that this position is correct.
addEmbedded(tlist[0].Pos(), parseUnion(check, tlist))
// All methods and embedded elements for this interface are collected;
// i.e., this interface is may be used in a type set computation.
ityp.complete = true
if len(ityp.methods) == 0 && len(ityp.embeddeds) == 0 {
// empty interface
ityp.tset = &topTypeSet
// sort for API stability
// (don't sort embeddeds: they must correspond to *embedPos entries)
// Compute type set with a non-nil *Checker as soon as possible
// to report any errors. Subsequent uses of type sets will use
// this computed type set and won't need to pass in a *Checker.
check.later(func() { computeInterfaceTypeSet(check, iface.Pos(), ityp) })
func flattenUnion(list []ast.Expr, x ast.Expr) []ast.Expr {
if o, _ := x.(*ast.BinaryExpr); o != nil && o.Op == token.OR {
list = flattenUnion(list, o.X)
x = o.Y
return append(list, x)