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// 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.
//go:build go1.18
// +build go1.18
package typeparams
import (
// GetIndexExprData extracts data from AST nodes that represent index
// expressions.
// For an ast.IndexExpr, the resulting IndexExprData will have exactly one
// index expression. For an ast.IndexListExpr (go1.18+), it may have a
// variable number of index expressions.
// For nodes that don't represent index expressions, GetIndexExprData returns
// nil.
func GetIndexExprData(n ast.Node) *IndexExprData {
switch e := n.(type) {
case *ast.IndexExpr:
return &IndexExprData{
X: e.X,
Lbrack: e.Lbrack,
Indices: []ast.Expr{e.Index},
Rbrack: e.Rbrack,
case *ast.IndexListExpr:
return (*IndexExprData)(e)
return nil
// PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on
// the cardinality of indices. Calling PackIndexExpr with len(indices) == 0
// will panic.
func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr {
switch len(indices) {
case 0:
panic("empty indices")
case 1:
return &ast.IndexExpr{
X: x,
Lbrack: lbrack,
Index: indices[0],
Rbrack: rbrack,
return &ast.IndexListExpr{
X: x,
Lbrack: lbrack,
Indices: indices,
Rbrack: rbrack,
// ForTypeSpec returns n.TypeParams.
func ForTypeSpec(n *ast.TypeSpec) *ast.FieldList {
if n == nil {
return nil
return n.TypeParams
// ForFuncType returns n.TypeParams.
func ForFuncType(n *ast.FuncType) *ast.FieldList {
if n == nil {
return nil
return n.TypeParams
// TypeParam is an alias for types.TypeParam
type TypeParam = types.TypeParam
// TypeParamList is an alias for types.TypeParamList
type TypeParamList = types.TypeParamList
// TypeList is an alias for types.TypeList
type TypeList = types.TypeList
// NewTypeParam calls types.NewTypeParam.
func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
return types.NewTypeParam(name, constraint)
// SetTypeParamConstraint calls tparam.SetConstraint(constraint).
func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
// ForSignature returns sig.TypeParams()
func ForSignature(sig *types.Signature) *TypeParamList {
return sig.TypeParams()
// SetForSignature calls sig.SetTypeParams(tparams)
func SetForSignature(sig *types.Signature, tparams []*TypeParam) {
// RecvTypeParams returns sig.RecvTypeParams().
func RecvTypeParams(sig *types.Signature) *TypeParamList {
return sig.RecvTypeParams()
// SetRecvTypeParams calls sig.SetRecvTypeParams(rparams).
func SetRecvTypeParams(sig *types.Signature, rparams []*TypeParam) {
// IsComparable calls iface.IsComparable().
func IsComparable(iface *types.Interface) bool {
return iface.IsComparable()
// IsConstraint calls iface.IsConstraint().
func IsConstraint(iface *types.Interface) bool {
return iface.IsConstraint()
// ForNamed extracts the (possibly empty) type parameter object list from
// named.
func ForNamed(named *types.Named) *TypeParamList {
return named.TypeParams()
// SetForNamed sets the type params tparams on n. Each tparam must be of
// dynamic type *types.TypeParam.
func SetForNamed(n *types.Named, tparams []*TypeParam) {
// NamedTypeArgs returns named.TypeArgs().
func NamedTypeArgs(named *types.Named) *TypeList {
return named.TypeArgs()
// NamedTypeOrigin returns named.Orig().
func NamedTypeOrigin(named *types.Named) types.Type {
return named.Origin()
// Term is an alias for types.Term.
type Term = types.Term
// NewTerm calls types.NewTerm.
func NewTerm(tilde bool, typ types.Type) *Term {
return types.NewTerm(tilde, typ)
// Union is an alias for types.Union
type Union = types.Union
// NewUnion calls types.NewUnion.
func NewUnion(terms []*Term) *Union {
return types.NewUnion(terms)
// InitInstanceInfo initializes info to record information about type and
// function instances.
func InitInstanceInfo(info *types.Info) {
info.Instances = make(map[*ast.Ident]types.Instance)
// GetInstance extracts information about the instantiation occurring at the
// identifier id. id should be the identifier denoting a parameterized type or
// function in an instantiation expression or function call.
func GetInstance(info *types.Info, id *ast.Ident) (*TypeList, types.Type) {
if info.Instances != nil {
inf := info.Instances[id]
return inf.TypeArgs, inf.Type
return nil, nil
// Environment is an alias for types.Environment.
type Environment = types.Environment
// Instantiate calls types.Instantiate.
func Instantiate(env *Environment, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
return types.Instantiate(env, typ, targs, validate)