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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 ssa
// This file defines a number of miscellaneous utility functions.
import (
//// AST utilities
func unparen(e ast.Expr) ast.Expr { return astutil.Unparen(e) }
// isBlankIdent returns true iff e is an Ident with name "_".
// They have no associated types.Object, and thus no type.
func isBlankIdent(e ast.Expr) bool {
id, ok := e.(*ast.Ident)
return ok && id.Name == "_"
//// Type utilities. Some of these belong in go/types.
// isPointer returns true for types whose underlying type is a pointer.
func isPointer(typ types.Type) bool {
_, ok := typ.Underlying().(*types.Pointer)
return ok
func isInterface(T types.Type) bool { return types.IsInterface(T) }
// deref returns a pointer's element type; otherwise it returns typ.
func deref(typ types.Type) types.Type {
if p, ok := typ.Underlying().(*types.Pointer); ok {
return p.Elem()
return typ
// recvType returns the receiver type of method obj.
func recvType(obj *types.Func) types.Type {
return obj.Type().(*types.Signature).Recv().Type()
// DefaultType returns the default "typed" type for an "untyped" type;
// it returns the incoming type for all other types. The default type
// for untyped nil is untyped nil.
// Exported to ssa/interp.
// TODO(adonovan): use go/types.DefaultType after 1.8.
func DefaultType(typ types.Type) types.Type {
if t, ok := typ.(*types.Basic); ok {
k := t.Kind()
switch k {
case types.UntypedBool:
k = types.Bool
case types.UntypedInt:
k = types.Int
case types.UntypedRune:
k = types.Rune
case types.UntypedFloat:
k = types.Float64
case types.UntypedComplex:
k = types.Complex128
case types.UntypedString:
k = types.String
typ = types.Typ[k]
return typ
// logStack prints the formatted "start" message to stderr and
// returns a closure that prints the corresponding "end" message.
// Call using 'defer logStack(...)()' to show builder stack on panic.
// Don't forget trailing parens!
func logStack(format string, args ...interface{}) func() {
msg := fmt.Sprintf(format, args...)
io.WriteString(os.Stderr, msg)
io.WriteString(os.Stderr, "\n")
return func() {
io.WriteString(os.Stderr, msg)
io.WriteString(os.Stderr, " end\n")
// newVar creates a 'var' for use in a types.Tuple.
func newVar(name string, typ types.Type) *types.Var {
return types.NewParam(token.NoPos, nil, name, typ)
// anonVar creates an anonymous 'var' for use in a types.Tuple.
func anonVar(typ types.Type) *types.Var {
return newVar("", typ)
var lenResults = types.NewTuple(anonVar(tInt))
// makeLen returns the len builtin specialized to type func(T)int.
func makeLen(T types.Type) *Builtin {
lenParams := types.NewTuple(anonVar(T))
return &Builtin{
name: "len",
sig: types.NewSignature(nil, lenParams, lenResults, false),