reflect: add Type.Bits method, add tags to prohibit conversions

gob: substitute slice for map

R=r
CC=golang-dev
https://golang.org/cl/1699045

9 files changed, 112 insertions, 144 deletions

diff --git a/src/pkg/fmt/print.go b/src/pkg/fmt/print.go
index 6ae7e5c2c2..bb2f08ea7b 100644
--- a/src/pkg/fmt/print.go
+++ b/src/pkg/fmt/print.go
@@ -612,10 +612,10 @@ func (p *pp) fmtUintptrGetter(field interface{}, value reflect.Value, verb int,
 }
 
 var (
-	intBits     = uintptr(reflect.Typeof(int(0)).Size() * 8)
-	floatBits   = uintptr(reflect.Typeof(float(0)).Size() * 8)
-	complexBits = uintptr(reflect.Typeof(complex(0+0i)).Size() * 8)
-	uintptrBits = uintptr(reflect.Typeof(uintptr(0)).Size() * 8)
+	intBits     = reflect.Typeof(0).Bits()
+	floatBits   = reflect.Typeof(0.0).Bits()
+	complexBits = reflect.Typeof(1i).Bits()
+	uintptrBits = reflect.Typeof(uintptr(0)).Bits()
 )
 
 func (p *pp) printField(field interface{}, verb int, plus, sharp bool, depth int) (was_string bool) {
diff --git a/src/pkg/fmt/scan.go b/src/pkg/fmt/scan.go
index 94383807a5..9f3b401173 100644
--- a/src/pkg/fmt/scan.go
+++ b/src/pkg/fmt/scan.go
@@ -456,9 +456,10 @@ func (s *ss) scanNumber(digits string) string {
 }
 
 // scanRune returns the next rune value in the input.
-func (s *ss) scanRune(bitSize uintptr) int64 {
+func (s *ss) scanRune(bitSize int) int64 {
 	rune := int64(s.mustGetRune())
-	x := (rune << (64 - bitSize)) >> (64 - bitSize)
+	n := uint(bitSize)
+	x := (rune << (64 - n)) >> (64 - n)
 	if x != rune {
 		s.errorString("overflow on character value " + string(rune))
 	}
@@ -467,7 +468,7 @@ func (s *ss) scanRune(bitSize uintptr) int64 {
 
 // scanInt returns the value of the integer represented by the next
 // token, checking for overflow.  Any error is stored in s.err.
-func (s *ss) scanInt(verb int, bitSize uintptr) int64 {
+func (s *ss) scanInt(verb int, bitSize int) int64 {
 	if verb == 'c' {
 		return s.scanRune(bitSize)
 	}
@@ -479,7 +480,8 @@ func (s *ss) scanInt(verb int, bitSize uintptr) int64 {
 	if err != nil {
 		s.error(err)
 	}
-	x := (i << (64 - bitSize)) >> (64 - bitSize)
+	n := uint(bitSize)
+	x := (i << (64 - n)) >> (64 - n)
 	if x != i {
 		s.errorString("integer overflow on token " + tok)
 	}
@@ -488,7 +490,7 @@ func (s *ss) scanInt(verb int, bitSize uintptr) int64 {
 
 // scanUint returns the value of the unsigned integer represented
 // by the next token, checking for overflow.  Any error is stored in s.err.
-func (s *ss) scanUint(verb int, bitSize uintptr) uint64 {
+func (s *ss) scanUint(verb int, bitSize int) uint64 {
 	if verb == 'c' {
 		return uint64(s.scanRune(bitSize))
 	}
@@ -499,7 +501,8 @@ func (s *ss) scanUint(verb int, bitSize uintptr) uint64 {
 	if err != nil {
 		s.error(err)
 	}
-	x := (i << (64 - bitSize)) >> (64 - bitSize)
+	n := uint(bitSize)
+	x := (i << (64 - n)) >> (64 - n)
 	if x != i {
 		s.errorString("unsigned integer overflow on token " + tok)
 	}
@@ -766,9 +769,9 @@ func (s *ss) scanOne(verb int, field interface{}) {
 		case *reflect.BoolValue:
 			v.Set(s.scanBool(verb))
 		case *reflect.IntValue:
-			v.Set(s.scanInt(verb, v.Type().Size()*8))
+			v.Set(s.scanInt(verb, v.Type().Bits()))
 		case *reflect.UintValue:
-			v.Set(s.scanUint(verb, v.Type().Size()*8))
+			v.Set(s.scanUint(verb, v.Type().Bits()))
 		case *reflect.StringValue:
 			v.Set(s.convertString(verb))
 		case *reflect.SliceValue:
@@ -784,9 +787,9 @@ func (s *ss) scanOne(verb int, field interface{}) {
 			}
 		case *reflect.FloatValue:
 			s.skipSpace()
-			v.Set(s.convertFloat(s.floatToken(), int(v.Type().Size()*8)))
+			v.Set(s.convertFloat(s.floatToken(), v.Type().Bits()))
 		case *reflect.ComplexValue:
-			v.Set(s.scanComplex(verb, int(v.Type().Size()*8)))
+			v.Set(s.scanComplex(verb, v.Type().Bits()))
 		default:
 		CantHandle:
 			s.errorString("Scan: can't handle type: " + val.Type().String())
diff --git a/src/pkg/gob/decode.go b/src/pkg/gob/decode.go
index 459acaf0b7..8f5c383ea9 100644
--- a/src/pkg/gob/decode.go
+++ b/src/pkg/gob/decode.go
@@ -540,7 +540,7 @@ func ignoreSlice(state *decodeState, elemOp decOp) os.Error {
 	return ignoreArrayHelper(state, elemOp, int(decodeUint(state)))
 }
 
-var decOpMap = map[reflect.Kind]decOp{
+var decOpMap = []decOp{
 	reflect.Bool:    decBool,
 	reflect.Int8:    decInt8,
 	reflect.Int16:   decInt16,
@@ -568,8 +568,12 @@ var decIgnoreOpMap = map[typeId]decOp{
 // the indirection count to reach it.
 func (dec *Decoder) decOpFor(wireId typeId, rt reflect.Type, name string) (decOp, int, os.Error) {
 	typ, indir := indirect(rt)
-	op, ok := decOpMap[typ.Kind()]
-	if !ok {
+	var op decOp
+	k := typ.Kind()
+	if int(k) < len(decOpMap) {
+		op = decOpMap[k]
+	}
+	if op == nil {
 		// Special cases
 		switch t := typ.(type) {
 		case *reflect.ArrayType:
diff --git a/src/pkg/gob/encode.go b/src/pkg/gob/encode.go
index 93f9e509b8..76032389e3 100644
--- a/src/pkg/gob/encode.go
+++ b/src/pkg/gob/encode.go
@@ -601,7 +601,7 @@ func encodeMap(b *bytes.Buffer, rt reflect.Type, p uintptr, keyOp, elemOp encOp,
 	return state.err
 }
 
-var encOpMap = map[reflect.Kind]encOp{
+var encOpMap = []encOp{
 	reflect.Bool:    encBool,
 	reflect.Int:     encInt,
 	reflect.Int8:    encInt8,
@@ -624,8 +624,12 @@ var encOpMap = map[reflect.Kind]encOp{
 // the indirection count to reach it.
 func encOpFor(rt reflect.Type) (encOp, int, os.Error) {
 	typ, indir := indirect(rt)
-	op, ok := encOpMap[typ.Kind()]
-	if !ok {
+	var op encOp
+	k := typ.Kind()
+	if int(k) < len(encOpMap) {
+		op = encOpMap[k]
+	}
+	if op == nil {
 		// Special cases
 		switch t := typ.(type) {
 		case *reflect.SliceType:
diff --git a/src/pkg/json/decode.go b/src/pkg/json/decode.go
index 6f768d4b8c..3f69650097 100644
--- a/src/pkg/json/decode.go
+++ b/src/pkg/json/decode.go
@@ -588,7 +588,7 @@ func (d *decodeState) literal(v reflect.Value) {
 			v.Set(n)
 
 		case *reflect.FloatValue:
-			n, err := strconv.AtofN(s, int(v.Type().Size()*8))
+			n, err := strconv.AtofN(s, v.Type().Bits())
 			if err != nil || v.Overflow(n) {
 				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
 				break
diff --git a/src/pkg/json/encode.go b/src/pkg/json/encode.go
index 8b0f784883..5d7ce35cbb 100644
--- a/src/pkg/json/encode.go
+++ b/src/pkg/json/encode.go
@@ -162,7 +162,7 @@ func (e *encodeState) reflectValue(v reflect.Value) {
 		e.WriteString(strconv.Uitoa64(v.Get()))
 
 	case *reflect.FloatValue:
-		e.WriteString(strconv.FtoaN(v.Get(), 'g', -1, int(v.Type().Size()*8)))
+		e.WriteString(strconv.FtoaN(v.Get(), 'g', -1, v.Type().Bits()))
 
 	case *reflect.StringValue:
 		e.string(v.Get())
diff --git a/src/pkg/reflect/type.go b/src/pkg/reflect/type.go
index 5fadcf2699..d87ccc984c 100644
--- a/src/pkg/reflect/type.go
+++ b/src/pkg/reflect/type.go
@@ -34,6 +34,11 @@ import (
  * copy in order to access the private fields.
  */
 
+// commonType is the common implementation of most values.
+// It is embedded in other, public struct types, but always
+// with a unique tag like "uint" or "float" so that the client cannot
+// convert from, say, *UintType to *FloatType.
+
 type commonType struct {
 	size       uintptr
 	hash       uint32
@@ -62,44 +67,44 @@ type uncommonType struct {
 
 // BoolType represents a boolean type.
 type BoolType struct {
-	commonType
+	commonType "bool"
 }
 
 // FloatType represents a float type.
 type FloatType struct {
-	commonType
+	commonType "float"
 }
 
 // ComplexType represents a complex type.
 type ComplexType struct {
-	commonType
+	commonType "complex"
 }
 
 // IntType represents a signed integer type.
 type IntType struct {
-	commonType
+	commonType "int"
 }
 
 // UintType represents a uint type.
 type UintType struct {
-	commonType
+	commonType "uint"
 }
 
 // StringType represents a string type.
 type StringType struct {
-	commonType
+	commonType "string"
 }
 
 // UnsafePointerType represents an unsafe.Pointer type.
 type UnsafePointerType struct {
-	commonType
+	commonType "unsafe.Pointer"
 }
 
 // ArrayType represents a fixed array type.
 type ArrayType struct {
-	commonType
-	elem *runtime.Type
-	len  uintptr
+	commonType "array"
+	elem       *runtime.Type
+	len        uintptr
 }
 
 // ChanDir represents a channel type's direction.
@@ -113,17 +118,17 @@ const (
 
 // ChanType represents a channel type.
 type ChanType struct {
-	commonType
-	elem *runtime.Type
-	dir  uintptr
+	commonType "chan"
+	elem       *runtime.Type
+	dir        uintptr
 }
 
 // FuncType represents a function type.
 type FuncType struct {
-	commonType
-	dotdotdot bool
-	in        []*runtime.Type
-	out       []*runtime.Type
+	commonType "func"
+	dotdotdot  bool
+	in         []*runtime.Type
+	out        []*runtime.Type
 }
 
 // Method on interface type
@@ -135,27 +140,27 @@ type imethod struct {
 
 // InterfaceType represents an interface type.
 type InterfaceType struct {
-	commonType
-	methods []imethod
+	commonType "interface"
+	methods    []imethod
 }
 
 // MapType represents a map type.
 type MapType struct {
-	commonType
-	key  *runtime.Type
-	elem *runtime.Type
+	commonType "map"
+	key        *runtime.Type
+	elem       *runtime.Type
 }
 
 // PtrType represents a pointer type.
 type PtrType struct {
-	commonType
-	elem *runtime.Type
+	commonType "ptr"
+	elem       *runtime.Type
 }
 
 // SliceType represents a slice type.
 type SliceType struct {
-	commonType
-	elem *runtime.Type
+	commonType "slice"
+	elem       *runtime.Type
 }
 
 // Struct field
@@ -169,8 +174,8 @@ type structField struct {
 
 // StructType represents a struct type.
 type StructType struct {
-	commonType
-	fields []structField
+	commonType "struct"
+	fields     []structField
 }
 
 
@@ -214,6 +219,11 @@ type Type interface {
 	// a value of the given type; it is analogous to unsafe.Sizeof.
 	Size() uintptr
 
+	// Bits returns the size of the type in bits.
+	// It is intended for use with numeric types and may overflow
+	// when used for composite types.
+	Bits() int
+
 	// Align returns the alignment of a value of this type
 	// when allocated in memory.
 	Align() int
@@ -333,6 +343,8 @@ func (t *commonType) String() string { return *t.string }
 
 func (t *commonType) Size() uintptr { return t.size }
 
+func (t *commonType) Bits() int { return int(t.size * 8) }
+
 func (t *commonType) Align() int { return int(t.align) }
 
 func (t *commonType) FieldAlign() int { return int(t.fieldAlign) }
@@ -352,7 +364,7 @@ func (t *uncommonType) Method(i int) (m Method) {
 	}
 	m.Type = toType(*p.typ).(*FuncType)
 	fn := p.tfn
-	m.Func = newFuncValue(m.Type, addr(&fn), true)
+	m.Func = &FuncValue{value: value{m.Type, addr(&fn), true}}
 	return
 }
 
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 5505c46241..56a5d69d86 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -75,6 +75,10 @@ type Value interface {
 	getAddr() addr
 }
 
+// value is the common implementation of most values.
+// It is embedded in other, public struct types, but always
+// with a unique tag like "uint" or "float" so that the client cannot
+// convert from, say, *UintValue to *FloatValue.
 type value struct {
 	typ    Type
 	addr   addr
@@ -113,7 +117,7 @@ func (v *value) CanSet() bool { return v.canSet }
 
 // BoolValue represents a bool value.
 type BoolValue struct {
-	value
+	value "bool"
 }
 
 // Get returns the underlying bool value.
@@ -132,7 +136,7 @@ func (v *BoolValue) SetValue(x Value) { v.Set(x.(*BoolValue).Get()) }
 
 // FloatValue represents a float value.
 type FloatValue struct {
-	value
+	value "float"
 }
 
 // Get returns the underlying int value.
@@ -181,7 +185,7 @@ func (v *FloatValue) SetValue(x Value) { v.Set(x.(*FloatValue).Get()) }
 
 // ComplexValue represents a complex value.
 type ComplexValue struct {
-	value
+	value "complex"
 }
 
 // Get returns the underlying complex value.
@@ -217,47 +221,9 @@ func (v *ComplexValue) Set(x complex128) {
 // Set sets v to the value x.
 func (v *ComplexValue) SetValue(x Value) { v.Set(x.(*ComplexValue).Get()) }
 
-// Complex64Value represents a complex64 value.
-type Complex64Value struct {
-	value
-}
-
-// Get returns the underlying complex64 value.
-func (v *Complex64Value) Get() complex64 { return *(*complex64)(v.addr) }
-
-// Set sets v to the value x.
-func (v *Complex64Value) Set(x complex64) {
-	if !v.canSet {
-		panic(cannotSet)
-	}
-	*(*complex64)(v.addr) = x
-}
-
-// Set sets v to the value x.
-func (v *Complex64Value) SetValue(x Value) { v.Set(x.(*Complex64Value).Get()) }
-
-// Complex128Value represents a complex128 value.
-type Complex128Value struct {
-	value
-}
-
-// Get returns the underlying complex128 value.
-func (v *Complex128Value) Get() complex128 { return *(*complex128)(v.addr) }
-
-// Set sets v to the value x.
-func (v *Complex128Value) Set(x complex128) {
-	if !v.canSet {
-		panic(cannotSet)
-	}
-	*(*complex128)(v.addr) = x
-}
-
-// Set sets v to the value x.
-func (v *Complex128Value) SetValue(x Value) { v.Set(x.(*Complex128Value).Get()) }
-
 // IntValue represents an int value.
 type IntValue struct {
-	value
+	value "int"
 }
 
 // Get returns the underlying int value.
@@ -303,7 +269,7 @@ func (v *IntValue) SetValue(x Value) { v.Set(x.(*IntValue).Get()) }
 
 // Overflow returns true if x cannot be represented by the type of v.
 func (v *IntValue) Overflow(x int64) bool {
-	bitSize := v.typ.Size() * 8
+	bitSize := uint(v.typ.Bits())
 	trunc := (x << (64 - bitSize)) >> (64 - bitSize)
 	return x != trunc
 }
@@ -316,7 +282,7 @@ type StringHeader struct {
 
 // StringValue represents a string value.
 type StringValue struct {
-	value
+	value "string"
 }
 
 // Get returns the underlying string value.
@@ -335,7 +301,7 @@ func (v *StringValue) SetValue(x Value) { v.Set(x.(*StringValue).Get()) }
 
 // UintValue represents a uint value.
 type UintValue struct {
-	value
+	value "uint"
 }
 
 // Get returns the underlying uuint value.
@@ -382,7 +348,7 @@ func (v *UintValue) Set(x uint64) {
 
 // Overflow returns true if x cannot be represented by the type of v.
 func (v *UintValue) Overflow(x uint64) bool {
-	bitSize := v.typ.Size() * 8
+	bitSize := uint(v.typ.Bits())
 	trunc := (x << (64 - bitSize)) >> (64 - bitSize)
 	return x != trunc
 }
@@ -392,7 +358,7 @@ func (v *UintValue) SetValue(x Value) { v.Set(x.(*UintValue).Get()) }
 
 // UnsafePointerValue represents an unsafe.Pointer value.
 type UnsafePointerValue struct {
-	value
+	value "unsafe.Pointer"
 }
 
 // Get returns the underlying uintptr value.
@@ -454,7 +420,7 @@ func ArrayCopy(dst, src ArrayOrSliceValue) int {
 
 // An ArrayValue represents an array.
 type ArrayValue struct {
-	value
+	value "array"
 }
 
 // Len returns the length of the array.
@@ -503,7 +469,7 @@ type SliceHeader struct {
 
 // A SliceValue represents a slice.
 type SliceValue struct {
-	value
+	value "slice"
 }
 
 func (v *SliceValue) slice() *SliceHeader { return (*SliceHeader)(v.value.addr) }
@@ -593,7 +559,7 @@ func MakeSlice(typ *SliceType, len, cap int) *SliceValue {
 
 // A ChanValue represents a chan.
 type ChanValue struct {
-	value
+	value "chan"
 }
 
 // IsNil returns whether v is a nil channel.
@@ -714,7 +680,7 @@ func MakeChan(typ *ChanType, buffer int) *ChanValue {
 
 // A FuncValue represents a function value.
 type FuncValue struct {
-	value
+	value       "func"
 	first       *value
 	isInterface bool
 }
@@ -874,7 +840,7 @@ func (fv *FuncValue) Call(in []Value) []Value {
 
 // An InterfaceValue represents an interface value.
 type InterfaceValue struct {
-	value
+	value "interface"
 }
 
 // No Get because v.Interface() is available.
@@ -939,7 +905,7 @@ func (v *InterfaceValue) Method(i int) *FuncValue {
 
 // A MapValue represents a map value.
 type MapValue struct {
-	value
+	value "map"
 }
 
 // IsNil returns whether v is a nil map value.
@@ -1056,7 +1022,7 @@ func MakeMap(typ *MapType) *MapValue {
 
 // A PtrValue represents a pointer.
 type PtrValue struct {
-	value
+	value "ptr"
 }
 
 // IsNil returns whether v is a nil pointer.
@@ -1127,7 +1093,7 @@ func Indirect(v Value) Value {
 
 // A StructValue represents a struct value.
 type StructValue struct {
-	value
+	value "struct"
 }
 
 // Set assigns x to v.
@@ -1211,57 +1177,39 @@ func NewValue(i interface{}) Value {
 	return newValue(toType(t), addr(a), true)
 }
 
-
-func newFuncValue(typ Type, addr addr, canSet bool) *FuncValue {
-	return &FuncValue{value: value{typ, addr, canSet}}
-}
-
 func newValue(typ Type, addr addr, canSet bool) Value {
-	// FuncValue has a different layout;
-	// it needs a extra space for the fixed receivers.
-	if _, ok := typ.(*FuncType); ok {
-		return newFuncValue(typ, addr, canSet)
-	}
-
-	// All values have same memory layout;
-	// build once and convert.
-	v := &struct{ value }{value{typ, addr, canSet}}
+	v := value{typ, addr, canSet}
 	switch typ.(type) {
 	case *ArrayType:
-		// TODO(rsc): Something must prevent
-		// clients of the package from doing
-		// this same kind of cast.
-		// We should be allowed because
-		// they're our types.
-		// Something about implicit assignment
-		// to struct fields.
-		return (*ArrayValue)(v)
+		return &ArrayValue{v}
 	case *BoolType:
-		return (*BoolValue)(v)
+		return &BoolValue{v}
 	case *ChanType:
-		return (*ChanValue)(v)
+		return &ChanValue{v}
 	case *FloatType:
-		return (*FloatValue)(v)
+		return &FloatValue{v}
+	case *FuncType:
+		return &FuncValue{value: v}
 	case *ComplexType:
-		return (*ComplexValue)(v)
+		return &ComplexValue{v}
 	case *IntType:
-		return (*IntValue)(v)
+		return &IntValue{v}
 	case *InterfaceType:
-		return (*InterfaceValue)(v)
+		return &InterfaceValue{v}
 	case *MapType:
-		return (*MapValue)(v)
+		return &MapValue{v}
 	case *PtrType:
-		return (*PtrValue)(v)
+		return &PtrValue{v}
 	case *SliceType:
-		return (*SliceValue)(v)
+		return &SliceValue{v}
 	case *StringType:
-		return (*StringValue)(v)
+		return &StringValue{v}
 	case *StructType:
-		return (*StructValue)(v)
+		return &StructValue{v}
 	case *UintType:
-		return (*UintValue)(v)
+		return &UintValue{v}
 	case *UnsafePointerType:
-		return (*UnsafePointerValue)(v)
+		return &UnsafePointerValue{v}
 	}
 	panic("newValue" + typ.String())
 }
diff --git a/test/ken/cplx3.go b/test/ken/cplx3.go
index 6c3826df6a..997894b418 100644
--- a/test/ken/cplx3.go
+++ b/test/ken/cplx3.go
@@ -30,9 +30,6 @@ func main() {
 
 	var a interface{}
 	switch c := reflect.NewValue(a).(type) {
-	case *reflect.Complex64Value:
-		v := c.Get()
-		_, _ = complex64(v), true
 	case *reflect.ComplexValue:
 		if complexBits == 64 {
 			v := c.Get()