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// Copyright 2012 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.
// This file implements typechecking of conversions.
package types
import (
"go/ast"
)
// conversion typechecks the type conversion conv to type typ. iota is the current
// value of iota or -1 if iota doesn't have a value in the current context. The result
// of the conversion is returned via x. If the conversion has type errors, the returned
// x is marked as invalid (x.mode == invalid).
//
func (check *checker) conversion(x *operand, conv *ast.CallExpr, typ Type, iota int) {
// all conversions have one argument
if len(conv.Args) != 1 {
check.invalidOp(conv.Pos(), "%s conversion requires exactly one argument", conv)
goto Error
}
// evaluate argument
check.expr(x, conv.Args[0], nil, iota)
if x.mode == invalid {
goto Error
}
if x.mode == constant && isConstType(typ) {
// constant conversion
// TODO(gri) implement this
} else {
// non-constant conversion
if !x.isConvertible(typ) {
check.invalidOp(conv.Pos(), "cannot convert %s to %s", x, typ)
goto Error
}
x.mode = value
}
x.expr = conv
x.typ = typ
return
Error:
x.mode = invalid
}
func (x *operand) isConvertible(T Type) bool {
// "x is assignable to T"
if x.isAssignable(T) {
return true
}
// "x's type and T have identical underlying types"
V := x.typ
Vu := underlying(V)
Tu := underlying(T)
if IsIdentical(Vu, Tu) {
return true
}
// "x's type and T are unnamed pointer types and their pointer base types have identical underlying types"
if V, ok := V.(*Pointer); ok {
if T, ok := T.(*Pointer); ok {
if IsIdentical(underlying(V.Base), underlying(T.Base)) {
return true
}
}
}
// "x's type and T are both integer or floating point types"
if (isInteger(V) || isFloat(V)) && (isInteger(T) || isFloat(T)) {
return true
}
// "x's type and T are both complex types"
if isComplex(V) && isComplex(T) {
return true
}
// "x is an integer or a slice of bytes or runes and T is a string type"
if (isInteger(V) || isBytesOrRunes(Vu)) && isString(T) {
return true
}
// "x is a string and T is a slice of bytes or runes"
if isString(V) && isBytesOrRunes(Tu) {
return true
}
// package unsafe:
// "any pointer or value of underlying type uintptr can be converted into a unsafe.Pointer"
if (isPointer(Vu) || isUintptr(Vu)) && isUnsafePointer(T) {
return true
}
// "and vice versa"
if isUnsafePointer(V) && (isPointer(Tu) || isUintptr(Tu)) {
return true
}
return false
}
func isUintptr(typ Type) bool {
t, ok := typ.(*Basic)
return ok && t.Kind == Uintptr
}
func isUnsafePointer(typ Type) bool {
t, ok := typ.(*Basic)
return ok && t.Kind == UnsafePointer
}
func isPointer(typ Type) bool {
_, ok := typ.(*Pointer)
return ok
}
func isBytesOrRunes(typ Type) bool {
if s, ok := typ.(*Slice); ok {
t, ok := underlying(s.Elt).(*Basic)
return ok && (t.Kind == Byte || t.Kind == Rune)
}
return false
}
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