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operand.go
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operand.go
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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 defines operands and associated operations.
package types
import (
"bytes"
"go/ast"
"go/constant"
"go/token"
)
// An operandMode specifies the (addressing) mode of an operand.
type operandMode byte
const (
invalid operandMode = iota // operand is invalid
novalue // operand represents no value (result of a function call w/o result)
builtin // operand is a built-in function
typexpr // operand is a type
constant_ // operand is a constant; the operand's typ is a Basic type
variable // operand is an addressable variable
mapindex // operand is a map index expression (acts like a variable on lhs, commaok on rhs of an assignment)
value // operand is a computed value
commaok // like value, but operand may be used in a comma,ok expression
)
var operandModeString = [...]string{
invalid: "invalid operand",
novalue: "no value",
builtin: "built-in",
typexpr: "type",
constant_: "constant",
variable: "variable",
mapindex: "map index expression",
value: "value",
commaok: "comma, ok expression",
}
// An operand represents an intermediate value during type checking.
// Operands have an (addressing) mode, the expression evaluating to
// the operand, the operand's type, a value for constants, and an id
// for built-in functions.
// The zero value of operand is a ready to use invalid operand.
//
type operand struct {
mode operandMode
expr ast.Expr
typ Type
val constant.Value
id builtinId
}
// pos returns the position of the expression corresponding to x.
// If x is invalid the position is token.NoPos.
//
func (x *operand) pos() token.Pos {
// x.expr may not be set if x is invalid
if x.expr == nil {
return token.NoPos
}
return x.expr.Pos()
}
// Operand string formats
// (not all "untyped" cases can appear due to the type system,
// but they fall out naturally here)
//
// mode format
//
// invalid <expr> ( <mode> )
// novalue <expr> ( <mode> )
// builtin <expr> ( <mode> )
// typexpr <expr> ( <mode> )
//
// constant <expr> (<untyped kind> <mode> )
// constant <expr> ( <mode> of type <typ>)
// constant <expr> (<untyped kind> <mode> <val> )
// constant <expr> ( <mode> <val> of type <typ>)
//
// variable <expr> (<untyped kind> <mode> )
// variable <expr> ( <mode> of type <typ>)
//
// mapindex <expr> (<untyped kind> <mode> )
// mapindex <expr> ( <mode> of type <typ>)
//
// value <expr> (<untyped kind> <mode> )
// value <expr> ( <mode> of type <typ>)
//
// commaok <expr> (<untyped kind> <mode> )
// commaok <expr> ( <mode> of type <typ>)
//
func operandString(x *operand, qf Qualifier) string {
var buf bytes.Buffer
var expr string
if x.expr != nil {
expr = ExprString(x.expr)
} else {
switch x.mode {
case builtin:
expr = predeclaredFuncs[x.id].name
case typexpr:
expr = TypeString(x.typ, qf)
case constant_:
expr = x.val.String()
}
}
// <expr> (
if expr != "" {
buf.WriteString(expr)
buf.WriteString(" (")
}
// <untyped kind>
hasType := false
switch x.mode {
case invalid, novalue, builtin, typexpr:
// no type
default:
// should have a type, but be cautious (don't crash during printing)
if x.typ != nil {
if isUntyped(x.typ) {
buf.WriteString(x.typ.(*Basic).name)
buf.WriteByte(' ')
break
}
hasType = true
}
}
// <mode>
buf.WriteString(operandModeString[x.mode])
// <val>
if x.mode == constant_ {
if s := x.val.String(); s != expr {
buf.WriteByte(' ')
buf.WriteString(s)
}
}
// <typ>
if hasType {
if x.typ != Typ[Invalid] {
buf.WriteString(" of type ")
WriteType(&buf, x.typ, qf)
} else {
buf.WriteString(" with invalid type")
}
}
// )
if expr != "" {
buf.WriteByte(')')
}
return buf.String()
}
func (x *operand) String() string {
return operandString(x, nil)
}
// setConst sets x to the untyped constant for literal lit.
func (x *operand) setConst(tok token.Token, lit string) {
var kind BasicKind
switch tok {
case token.INT:
kind = UntypedInt
case token.FLOAT:
kind = UntypedFloat
case token.IMAG:
kind = UntypedComplex
case token.CHAR:
kind = UntypedRune
case token.STRING:
kind = UntypedString
default:
unreachable()
}
x.mode = constant_
x.typ = Typ[kind]
x.val = constant.MakeFromLiteral(lit, tok, 0)
}
// isNil reports whether x is the nil value.
func (x *operand) isNil() bool {
return x.mode == value && x.typ == Typ[UntypedNil]
}
// TODO(gri) The functions operand.assignableTo, checker.convertUntyped,
// checker.representable, and checker.assignment are
// overlapping in functionality. Need to simplify and clean up.
// assignableTo reports whether x is assignable to a variable of type T.
// If the result is false and a non-nil reason is provided, it may be set
// to a more detailed explanation of the failure (result != "").
func (x *operand) assignableTo(conf *Config, T Type, reason *string) bool {
if x.mode == invalid || T == Typ[Invalid] {
return true // avoid spurious errors
}
V := x.typ
// x's type is identical to T
if Identical(V, T) {
return true
}
Vu := V.Underlying()
Tu := T.Underlying()
// x is an untyped value representable by a value of type T
// TODO(gri) This is borrowing from checker.convertUntyped and
// checker.representable. Need to clean up.
if isUntyped(Vu) {
switch t := Tu.(type) {
case *Basic:
if x.isNil() && t.kind == UnsafePointer {
return true
}
if x.mode == constant_ {
return representableConst(x.val, conf, t, nil)
}
// The result of a comparison is an untyped boolean,
// but may not be a constant.
if Vb, _ := Vu.(*Basic); Vb != nil {
return Vb.kind == UntypedBool && isBoolean(Tu)
}
case *Interface:
return x.isNil() || t.Empty()
case *Pointer, *Signature, *Slice, *Map, *Chan:
return x.isNil()
}
}
// Vu is typed
// x's type V and T have identical underlying types
// and at least one of V or T is not a named type
if Identical(Vu, Tu) && (!isNamed(V) || !isNamed(T)) {
return true
}
// T is an interface type and x implements T
if Ti, ok := Tu.(*Interface); ok {
if m, wrongType := MissingMethod(x.typ, Ti, true); m != nil /* Implements(x.typ, Ti) */ {
if reason != nil {
if wrongType {
*reason = "wrong type for method " + m.Name()
} else {
*reason = "missing method " + m.Name()
}
}
return false
}
return true
}
// x is a bidirectional channel value, T is a channel
// type, x's type V and T have identical element types,
// and at least one of V or T is not a named type
if Vc, ok := Vu.(*Chan); ok && Vc.dir == SendRecv {
if Tc, ok := Tu.(*Chan); ok && Identical(Vc.elem, Tc.elem) {
return !isNamed(V) || !isNamed(T)
}
}
return false
}