Example #1
0
// MethodSet returns the method set of type T.  It is thread-safe.
//
// If cache is nil, this function is equivalent to types.NewMethodSet(T).
// Utility functions can thus expose an optional *MethodSetCache
// parameter to clients that care about performance.
//
func (cache *MethodSetCache) MethodSet(T types.Type) *types.MethodSet {
	if cache == nil {
		return types.NewMethodSet(T)
	}
	cache.mu.Lock()
	defer cache.mu.Unlock()

	switch T := T.(type) {
	case *types.Named:
		return cache.lookupNamed(T).value

	case *types.Pointer:
		if N, ok := T.Elem().(*types.Named); ok {
			return cache.lookupNamed(N).pointer
		}
	}

	// all other types
	// (The map uses pointer equivalence, not type identity.)
	mset := cache.others[T]
	if mset == nil {
		mset = types.NewMethodSet(T)
		if cache.others == nil {
			cache.others = make(map[types.Type]*types.MethodSet)
		}
		cache.others[T] = mset
	}
	return mset
}
Example #2
0
func (x array) hash(t types.Type) int {
	h := 0
	tElt := t.Underlying().(*types.Array).Elem()
	for _, xi := range x {
		h += hash(tElt, xi)
	}
	return h
}
Example #3
0
func (x structure) hash(t types.Type) int {
	tStruct := t.Underlying().(*types.Struct)
	h := 0
	for i, n := 0, tStruct.NumFields(); i < n; i++ {
		if f := tStruct.Field(i); !f.Anonymous() {
			h += hash(f.Type(), x[i])
		}
	}
	return h
}
Example #4
0
func (x array) eq(t types.Type, _y interface{}) bool {
	y := _y.(array)
	tElt := t.Underlying().(*types.Array).Elem()
	for i, xi := range x {
		if !equals(tElt, xi, y[i]) {
			return false
		}
	}
	return true
}
Example #5
0
// usesBuiltinMap returns true if the built-in hash function and
// equivalence relation for type t are consistent with those of the
// interpreter's representation of type t.  Such types are: all basic
// types (bool, numbers, string), pointers and channels.
//
// usesBuiltinMap returns false for types that require a custom map
// implementation: interfaces, arrays and structs.
//
// Panic ensues if t is an invalid map key type: function, map or slice.
func usesBuiltinMap(t types.Type) bool {
	switch t := t.(type) {
	case *types.Basic, *types.Chan, *types.Pointer:
		return true
	case *types.Named:
		return usesBuiltinMap(t.Underlying())
	case *types.Interface, *types.Array, *types.Struct:
		return false
	}
	panic(fmt.Sprintf("invalid map key type: %T", t))
}
Example #6
0
func (x structure) eq(t types.Type, _y interface{}) bool {
	y := _y.(structure)
	tStruct := t.Underlying().(*types.Struct)
	for i, n := 0, tStruct.NumFields(); i < n; i++ {
		if f := tStruct.Field(i); !f.Anonymous() {
			if !equals(f.Type(), x[i], y[i]) {
				return false
			}
		}
	}
	return true
}
Example #7
0
// CanHaveDynamicTypes reports whether the type T can "hold" dynamic types,
// i.e. is an interface (incl. reflect.Type) or a reflect.Value.
//
func CanHaveDynamicTypes(T types.Type) bool {
	switch T := T.(type) {
	case *types.Named:
		if obj := T.Obj(); obj.Name() == "Value" && obj.Pkg().Path() == "reflect" {
			return true // reflect.Value
		}
		return CanHaveDynamicTypes(T.Underlying())
	case *types.Interface:
		return true
	}
	return false
}
Example #8
0
// CanPoint reports whether the type T is pointerlike,
// for the purposes of this analysis.
func CanPoint(T types.Type) bool {
	switch T := T.(type) {
	case *types.Named:
		if obj := T.Obj(); obj.Name() == "Value" && obj.Pkg().Path() == "reflect" {
			return true // treat reflect.Value like interface{}
		}
		return CanPoint(T.Underlying())

	case *types.Pointer, *types.Interface, *types.Map, *types.Chan, *types.Signature, *types.Slice:
		return true
	}

	return false // array struct tuple builtin basic
}
Example #9
0
// eqnil returns the comparison x == y using the equivalence relation
// appropriate for type t.
// If t is a reference type, at most one of x or y may be a nil value
// of that type.
//
func eqnil(t types.Type, x, y value) bool {
	switch t.Underlying().(type) {
	case *types.Map, *types.Signature, *types.Slice:
		// Since these types don't support comparison,
		// one of the operands must be a literal nil.
		switch x := x.(type) {
		case *hashmap:
			return (x != nil) == (y.(*hashmap) != nil)
		case map[value]value:
			return (x != nil) == (y.(map[value]value) != nil)
		case *ssa.Function:
			switch y := y.(type) {
			case *ssa.Function:
				return (x != nil) == (y != nil)
			case *closure:
				return true
			}
		case *closure:
			return (x != nil) == (y.(*ssa.Function) != nil)
		case []value:
			return (x != nil) == (y.([]value) != nil)
		}
		panic(fmt.Sprintf("eqnil(%s): illegal dynamic type: %T", t, x))
	}

	return equals(t, x, y)
}
Example #10
0
// zeroValue emits to f code to produce a zero value of type t,
// and returns it.
//
func zeroValue(f *Function, t types.Type) Value {
	switch t.Underlying().(type) {
	case *types.Struct, *types.Array:
		return emitLoad(f, f.addLocal(t, token.NoPos))
	default:
		return zeroConst(t)
	}
}
Example #11
0
// store stores value v of type T into *addr.
func store(T types.Type, addr *value, v value) {
	switch T := T.Underlying().(type) {
	case *types.Struct:
		lhs := (*addr).(structure)
		rhs := v.(structure)
		for i := range lhs {
			store(T.Field(i).Type(), &lhs[i], rhs[i])
		}
	case *types.Array:
		lhs := (*addr).(array)
		rhs := v.(array)
		for i := range lhs {
			store(T.Elem(), &lhs[i], rhs[i])
		}
	default:
		*addr = v
	}
}
Example #12
0
// IntuitiveMethodSet returns the intuitive method set of a type, T.
//
// The result contains MethodSet(T) and additionally, if T is a
// concrete type, methods belonging to *T if there is no identically
// named method on T itself.  This corresponds to user intuition about
// method sets; this function is intended only for user interfaces.
//
// The order of the result is as for types.MethodSet(T).
//
func IntuitiveMethodSet(T types.Type, msets *MethodSetCache) []*types.Selection {
	var result []*types.Selection
	mset := msets.MethodSet(T)
	if _, ok := T.Underlying().(*types.Interface); ok {
		for i, n := 0, mset.Len(); i < n; i++ {
			result = append(result, mset.At(i))
		}
	} else {
		pmset := msets.MethodSet(types.NewPointer(T))
		for i, n := 0, pmset.Len(); i < n; i++ {
			meth := pmset.At(i)
			if m := mset.Lookup(meth.Obj().Pkg(), meth.Obj().Name()); m != nil {
				meth = m
			}
			result = append(result, meth)
		}
	}
	return result
}
Example #13
0
// load returns the value of type T in *addr.
func load(T types.Type, addr *value) value {
	switch T := T.Underlying().(type) {
	case *types.Struct:
		v := (*addr).(structure)
		a := make(structure, len(v))
		for i := range a {
			a[i] = load(T.Field(i).Type(), &v[i])
		}
		return a
	case *types.Array:
		v := (*addr).(array)
		a := make(array, len(v))
		for i := range a {
			a[i] = load(T.Elem(), &v[i])
		}
		return a
	default:
		return *addr
	}
}
Example #14
0
// offsetOf returns the (abstract) offset of field index within struct
// or tuple typ.
func (a *analysis) offsetOf(typ types.Type, index int) uint32 {
	var offset uint32
	switch t := typ.Underlying().(type) {
	case *types.Tuple:
		for i := 0; i < index; i++ {
			offset += a.sizeof(t.At(i).Type())
		}
	case *types.Struct:
		offset++ // the node for the struct itself
		for i := 0; i < index; i++ {
			offset += a.sizeof(t.Field(i).Type())
		}
	default:
		panic(fmt.Sprintf("offsetOf(%s : %T)", typ, typ))
	}
	return offset
}
Example #15
0
// sliceToArray returns the type representing the arrays to which
// slice type slice points.
func sliceToArray(slice types.Type) *types.Array {
	return types.NewArray(slice.Underlying().(*types.Slice).Elem(), 1)
}
Example #16
0
// addRuntimeType is called for each concrete type that can be the
// dynamic type of some interface or reflect.Value.
// Adapted from needMethods in go/ssa/builder.go
//
func (r *rta) addRuntimeType(T types.Type, skip bool) {
	if prev, ok := r.result.RuntimeTypes.At(T).(bool); ok {
		if skip && !prev {
			r.result.RuntimeTypes.Set(T, skip)
		}
		return
	}
	r.result.RuntimeTypes.Set(T, skip)

	mset := r.prog.MethodSets.MethodSet(T)

	if _, ok := T.Underlying().(*types.Interface); !ok {
		// T is a new concrete type.
		for i, n := 0, mset.Len(); i < n; i++ {
			sel := mset.At(i)
			m := sel.Obj()

			if m.Exported() {
				// Exported methods are always potentially callable via reflection.
				r.addReachable(r.prog.MethodValue(sel), true)
			}
		}

		// Add callgraph edge for each existing dynamic
		// "invoke"-mode call via that interface.
		for _, I := range r.interfaces(T) {
			sites, _ := r.invokeSites.At(I).([]ssa.CallInstruction)
			for _, site := range sites {
				r.addInvokeEdge(site, T)
			}
		}
	}

	// Precondition: T is not a method signature (*Signature with Recv()!=nil).
	// Recursive case: skip => don't call makeMethods(T).
	// Each package maintains its own set of types it has visited.

	var n *types.Named
	switch T := T.(type) {
	case *types.Named:
		n = T
	case *types.Pointer:
		n, _ = T.Elem().(*types.Named)
	}
	if n != nil {
		owner := n.Obj().Pkg()
		if owner == nil {
			return // built-in error type
		}
	}

	// Recursion over signatures of each exported method.
	for i := 0; i < mset.Len(); i++ {
		if mset.At(i).Obj().Exported() {
			sig := mset.At(i).Type().(*types.Signature)
			r.addRuntimeType(sig.Params(), true)  // skip the Tuple itself
			r.addRuntimeType(sig.Results(), true) // skip the Tuple itself
		}
	}

	switch t := T.(type) {
	case *types.Basic:
		// nop

	case *types.Interface:
		// nop---handled by recursion over method set.

	case *types.Pointer:
		r.addRuntimeType(t.Elem(), false)

	case *types.Slice:
		r.addRuntimeType(t.Elem(), false)

	case *types.Chan:
		r.addRuntimeType(t.Elem(), false)

	case *types.Map:
		r.addRuntimeType(t.Key(), false)
		r.addRuntimeType(t.Elem(), false)

	case *types.Signature:
		if t.Recv() != nil {
			panic(fmt.Sprintf("Signature %s has Recv %s", t, t.Recv()))
		}
		r.addRuntimeType(t.Params(), true)  // skip the Tuple itself
		r.addRuntimeType(t.Results(), true) // skip the Tuple itself

	case *types.Named:
		// A pointer-to-named type can be derived from a named
		// type via reflection.  It may have methods too.
		r.addRuntimeType(types.NewPointer(T), false)

		// Consider 'type T struct{S}' where S has methods.
		// Reflection provides no way to get from T to struct{S},
		// only to S, so the method set of struct{S} is unwanted,
		// so set 'skip' flag during recursion.
		r.addRuntimeType(t.Underlying(), true)

	case *types.Array:
		r.addRuntimeType(t.Elem(), false)

	case *types.Struct:
		for i, n := 0, t.NumFields(); i < n; i++ {
			r.addRuntimeType(t.Field(i).Type(), false)
		}

	case *types.Tuple:
		for i, n := 0, t.Len(); i < n; i++ {
			r.addRuntimeType(t.At(i).Type(), false)
		}

	default:
		panic(T)
	}
}
Example #17
0
// flatten returns a list of directly contained fields in the preorder
// traversal of the type tree of t.  The resulting elements are all
// scalars (basic types or pointerlike types), except for struct/array
// "identity" nodes, whose type is that of the aggregate.
//
// reflect.Value is considered pointerlike, similar to interface{}.
//
// Callers must not mutate the result.
//
func (a *analysis) flatten(t types.Type) []*fieldInfo {
	fl, ok := a.flattenMemo[t]
	if !ok {
		switch t := t.(type) {
		case *types.Named:
			u := t.Underlying()
			if isInterface(u) {
				// Debuggability hack: don't remove
				// the named type from interfaces as
				// they're very verbose.
				fl = append(fl, &fieldInfo{typ: t})
			} else {
				fl = a.flatten(u)
			}

		case *types.Basic,
			*types.Signature,
			*types.Chan,
			*types.Map,
			*types.Interface,
			*types.Slice,
			*types.Pointer:
			fl = append(fl, &fieldInfo{typ: t})

		case *types.Array:
			fl = append(fl, &fieldInfo{typ: t}) // identity node
			for _, fi := range a.flatten(t.Elem()) {
				fl = append(fl, &fieldInfo{typ: fi.typ, op: true, tail: fi})
			}

		case *types.Struct:
			fl = append(fl, &fieldInfo{typ: t}) // identity node
			for i, n := 0, t.NumFields(); i < n; i++ {
				f := t.Field(i)
				for _, fi := range a.flatten(f.Type()) {
					fl = append(fl, &fieldInfo{typ: fi.typ, op: f, tail: fi})
				}
			}

		case *types.Tuple:
			// No identity node: tuples are never address-taken.
			n := t.Len()
			if n == 1 {
				// Don't add a fieldInfo link for singletons,
				// e.g. in params/results.
				fl = append(fl, a.flatten(t.At(0).Type())...)
			} else {
				for i := 0; i < n; i++ {
					f := t.At(i)
					for _, fi := range a.flatten(f.Type()) {
						fl = append(fl, &fieldInfo{typ: fi.typ, op: i, tail: fi})
					}
				}
			}

		default:
			panic(t)
		}

		a.flattenMemo[t] = fl
	}

	return fl
}
Example #18
0
// hashFor computes the hash of t.
func (h Hasher) hashFor(t types.Type) uint32 {
	// See Identical for rationale.
	switch t := t.(type) {
	case *types.Basic:
		return uint32(t.Kind())

	case *types.Array:
		return 9043 + 2*uint32(t.Len()) + 3*h.Hash(t.Elem())

	case *types.Slice:
		return 9049 + 2*h.Hash(t.Elem())

	case *types.Struct:
		var hash uint32 = 9059
		for i, n := 0, t.NumFields(); i < n; i++ {
			f := t.Field(i)
			if f.Anonymous() {
				hash += 8861
			}
			hash += hashString(t.Tag(i))
			hash += hashString(f.Name()) // (ignore f.Pkg)
			hash += h.Hash(f.Type())
		}
		return hash

	case *types.Pointer:
		return 9067 + 2*h.Hash(t.Elem())

	case *types.Signature:
		var hash uint32 = 9091
		if t.Variadic() {
			hash *= 8863
		}
		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())

	case *types.Interface:
		var hash uint32 = 9103
		for i, n := 0, t.NumMethods(); i < n; i++ {
			// See go/types.identicalMethods for rationale.
			// Method order is not significant.
			// Ignore m.Pkg().
			m := t.Method(i)
			hash += 3*hashString(m.Name()) + 5*h.Hash(m.Type())
		}
		return hash

	case *types.Map:
		return 9109 + 2*h.Hash(t.Key()) + 3*h.Hash(t.Elem())

	case *types.Chan:
		return 9127 + 2*uint32(t.Dir()) + 3*h.Hash(t.Elem())

	case *types.Named:
		// Not safe with a copying GC; objects may move.
		return uint32(reflect.ValueOf(t.Obj()).Pointer())

	case *types.Tuple:
		return h.hashTuple(t)
	}
	panic(t)
}
Example #19
0
// zero returns a new "zero" value of the specified type.
func zero(t types.Type) value {
	switch t := t.(type) {
	case *types.Basic:
		if t.Kind() == types.UntypedNil {
			panic("untyped nil has no zero value")
		}
		if t.Info()&types.IsUntyped != 0 {
			// TODO(adonovan): make it an invariant that
			// this is unreachable.  Currently some
			// constants have 'untyped' types when they
			// should be defaulted by the typechecker.
			t = ssa.DefaultType(t).(*types.Basic)
		}
		switch t.Kind() {
		case types.Bool:
			return false
		case types.Int:
			return int(0)
		case types.Int8:
			return int8(0)
		case types.Int16:
			return int16(0)
		case types.Int32:
			return int32(0)
		case types.Int64:
			return int64(0)
		case types.Uint:
			return uint(0)
		case types.Uint8:
			return uint8(0)
		case types.Uint16:
			return uint16(0)
		case types.Uint32:
			return uint32(0)
		case types.Uint64:
			return uint64(0)
		case types.Uintptr:
			return uintptr(0)
		case types.Float32:
			return float32(0)
		case types.Float64:
			return float64(0)
		case types.Complex64:
			return complex64(0)
		case types.Complex128:
			return complex128(0)
		case types.String:
			return ""
		case types.UnsafePointer:
			return unsafe.Pointer(nil)
		default:
			panic(fmt.Sprint("zero for unexpected type:", t))
		}
	case *types.Pointer:
		return (*value)(nil)
	case *types.Array:
		a := make(array, t.Len())
		for i := range a {
			a[i] = zero(t.Elem())
		}
		return a
	case *types.Named:
		return zero(t.Underlying())
	case *types.Interface:
		return iface{} // nil type, methodset and value
	case *types.Slice:
		return []value(nil)
	case *types.Struct:
		s := make(structure, t.NumFields())
		for i := range s {
			s[i] = zero(t.Field(i).Type())
		}
		return s
	case *types.Tuple:
		if t.Len() == 1 {
			return zero(t.At(0).Type())
		}
		s := make(tuple, t.Len())
		for i := range s {
			s[i] = zero(t.At(i).Type())
		}
		return s
	case *types.Chan:
		return chan value(nil)
	case *types.Map:
		if usesBuiltinMap(t.Key()) {
			return map[value]value(nil)
		}
		return (*hashmap)(nil)
	case *types.Signature:
		return (*ssa.Function)(nil)
	}
	panic(fmt.Sprint("zero: unexpected ", t))
}
Example #20
0
// mustDeref returns the element type of its argument, which must be a
// pointer; panic ensues otherwise.
func mustDeref(typ types.Type) types.Type {
	return typ.Underlying().(*types.Pointer).Elem()
}
Example #21
0
// 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
}
Example #22
0
// zeroConst returns a new "zero" constant of the specified type,
// which must not be an array or struct type: the zero values of
// aggregates are well-defined but cannot be represented by Const.
//
func zeroConst(t types.Type) *Const {
	switch t := t.(type) {
	case *types.Basic:
		switch {
		case t.Info()&types.IsBoolean != 0:
			return NewConst(exact.MakeBool(false), t)
		case t.Info()&types.IsNumeric != 0:
			return NewConst(exact.MakeInt64(0), t)
		case t.Info()&types.IsString != 0:
			return NewConst(exact.MakeString(""), t)
		case t.Kind() == types.UnsafePointer:
			fallthrough
		case t.Kind() == types.UntypedNil:
			return nilConst(t)
		default:
			panic(fmt.Sprint("zeroConst for unexpected type:", t))
		}
	case *types.Pointer, *types.Slice, *types.Interface, *types.Chan, *types.Map, *types.Signature:
		return nilConst(t)
	case *types.Named:
		return NewConst(zeroConst(t.Underlying()).Value, t)
	case *types.Array, *types.Struct, *types.Tuple:
		panic(fmt.Sprint("zeroConst applied to aggregate:", t))
	}
	panic(fmt.Sprint("zeroConst: unexpected ", t))
}
Example #23
0
// emitConv emits to f code to convert Value val to exactly type typ,
// and returns the converted value.  Implicit conversions are required
// by language assignability rules in assignments, parameter passing,
// etc.  Conversions cannot fail dynamically.
//
func emitConv(f *Function, val Value, typ types.Type) Value {
	t_src := val.Type()

	// Identical types?  Conversion is a no-op.
	if types.Identical(t_src, typ) {
		return val
	}

	ut_dst := typ.Underlying()
	ut_src := t_src.Underlying()

	// Just a change of type, but not value or representation?
	if isValuePreserving(ut_src, ut_dst) {
		c := &ChangeType{X: val}
		c.setType(typ)
		return f.emit(c)
	}

	// Conversion to, or construction of a value of, an interface type?
	if _, ok := ut_dst.(*types.Interface); ok {
		// Assignment from one interface type to another?
		if _, ok := ut_src.(*types.Interface); ok {
			c := &ChangeInterface{X: val}
			c.setType(typ)
			return f.emit(c)
		}

		// Untyped nil constant?  Return interface-typed nil constant.
		if ut_src == tUntypedNil {
			return nilConst(typ)
		}

		// Convert (non-nil) "untyped" literals to their default type.
		if t, ok := ut_src.(*types.Basic); ok && t.Info()&types.IsUntyped != 0 {
			val = emitConv(f, val, DefaultType(ut_src))
		}

		f.Pkg.Prog.needMethodsOf(val.Type())
		mi := &MakeInterface{X: val}
		mi.setType(typ)
		return f.emit(mi)
	}

	// Conversion of a compile-time constant value?
	if c, ok := val.(*Const); ok {
		if _, ok := ut_dst.(*types.Basic); ok || c.IsNil() {
			// Conversion of a compile-time constant to
			// another constant type results in a new
			// constant of the destination type and
			// (initially) the same abstract value.
			// We don't truncate the value yet.
			return NewConst(c.Value, typ)
		}

		// We're converting from constant to non-constant type,
		// e.g. string -> []byte/[]rune.
	}

	// A representation-changing conversion?
	// At least one of {ut_src,ut_dst} must be *Basic.
	// (The other may be []byte or []rune.)
	_, ok1 := ut_src.(*types.Basic)
	_, ok2 := ut_dst.(*types.Basic)
	if ok1 || ok2 {
		c := &Convert{X: val}
		c.setType(typ)
		return f.emit(c)
	}

	panic(fmt.Sprintf("in %s: cannot convert %s (%s) to %s", f, val, val.Type(), typ))
}
Example #24
0
// isPointer returns true for types whose underlying type is a pointer.
func isPointer(typ types.Type) bool {
	_, ok := typ.Underlying().(*types.Pointer)
	return ok
}
Example #25
0
func reflectKind(t types.Type) reflect.Kind {
	switch t := t.(type) {
	case *types.Named:
		return reflectKind(t.Underlying())
	case *types.Basic:
		switch t.Kind() {
		case types.Bool:
			return reflect.Bool
		case types.Int:
			return reflect.Int
		case types.Int8:
			return reflect.Int8
		case types.Int16:
			return reflect.Int16
		case types.Int32:
			return reflect.Int32
		case types.Int64:
			return reflect.Int64
		case types.Uint:
			return reflect.Uint
		case types.Uint8:
			return reflect.Uint8
		case types.Uint16:
			return reflect.Uint16
		case types.Uint32:
			return reflect.Uint32
		case types.Uint64:
			return reflect.Uint64
		case types.Uintptr:
			return reflect.Uintptr
		case types.Float32:
			return reflect.Float32
		case types.Float64:
			return reflect.Float64
		case types.Complex64:
			return reflect.Complex64
		case types.Complex128:
			return reflect.Complex128
		case types.String:
			return reflect.String
		case types.UnsafePointer:
			return reflect.UnsafePointer
		}
	case *types.Array:
		return reflect.Array
	case *types.Chan:
		return reflect.Chan
	case *types.Signature:
		return reflect.Func
	case *types.Interface:
		return reflect.Interface
	case *types.Map:
		return reflect.Map
	case *types.Pointer:
		return reflect.Ptr
	case *types.Slice:
		return reflect.Slice
	case *types.Struct:
		return reflect.Struct
	}
	panic(fmt.Sprint("unexpected type: ", t))
}
Example #26
0
// conv converts the value x of type t_src to type t_dst and returns
// the result.
// Possible cases are described with the ssa.Convert operator.
//
func conv(t_dst, t_src types.Type, x value) value {
	ut_src := t_src.Underlying()
	ut_dst := t_dst.Underlying()

	// Destination type is not an "untyped" type.
	if b, ok := ut_dst.(*types.Basic); ok && b.Info()&types.IsUntyped != 0 {
		panic("oops: conversion to 'untyped' type: " + b.String())
	}

	// Nor is it an interface type.
	if _, ok := ut_dst.(*types.Interface); ok {
		if _, ok := ut_src.(*types.Interface); ok {
			panic("oops: Convert should be ChangeInterface")
		} else {
			panic("oops: Convert should be MakeInterface")
		}
	}

	// Remaining conversions:
	//    + untyped string/number/bool constant to a specific
	//      representation.
	//    + conversions between non-complex numeric types.
	//    + conversions between complex numeric types.
	//    + integer/[]byte/[]rune -> string.
	//    + string -> []byte/[]rune.
	//
	// All are treated the same: first we extract the value to the
	// widest representation (int64, uint64, float64, complex128,
	// or string), then we convert it to the desired type.

	switch ut_src := ut_src.(type) {
	case *types.Pointer:
		switch ut_dst := ut_dst.(type) {
		case *types.Basic:
			// *value to unsafe.Pointer?
			if ut_dst.Kind() == types.UnsafePointer {
				return unsafe.Pointer(x.(*value))
			}
		}

	case *types.Slice:
		// []byte or []rune -> string
		// TODO(adonovan): fix: type B byte; conv([]B -> string).
		switch ut_src.Elem().(*types.Basic).Kind() {
		case types.Byte:
			x := x.([]value)
			b := make([]byte, 0, len(x))
			for i := range x {
				b = append(b, x[i].(byte))
			}
			return string(b)

		case types.Rune:
			x := x.([]value)
			r := make([]rune, 0, len(x))
			for i := range x {
				r = append(r, x[i].(rune))
			}
			return string(r)
		}

	case *types.Basic:
		x = widen(x)

		// integer -> string?
		// TODO(adonovan): fix: test integer -> named alias of string.
		if ut_src.Info()&types.IsInteger != 0 {
			if ut_dst, ok := ut_dst.(*types.Basic); ok && ut_dst.Kind() == types.String {
				return string(asInt(x))
			}
		}

		// string -> []rune, []byte or string?
		if s, ok := x.(string); ok {
			switch ut_dst := ut_dst.(type) {
			case *types.Slice:
				var res []value
				// TODO(adonovan): fix: test named alias of rune, byte.
				switch ut_dst.Elem().(*types.Basic).Kind() {
				case types.Rune:
					for _, r := range []rune(s) {
						res = append(res, r)
					}
					return res
				case types.Byte:
					for _, b := range []byte(s) {
						res = append(res, b)
					}
					return res
				}
			case *types.Basic:
				if ut_dst.Kind() == types.String {
					return x.(string)
				}
			}
			break // fail: no other conversions for string
		}

		// unsafe.Pointer -> *value
		if ut_src.Kind() == types.UnsafePointer {
			// TODO(adonovan): this is wrong and cannot
			// really be fixed with the current design.
			//
			// return (*value)(x.(unsafe.Pointer))
			// creates a new pointer of a different
			// type but the underlying interface value
			// knows its "true" type and so cannot be
			// meaningfully used through the new pointer.
			//
			// To make this work, the interpreter needs to
			// simulate the memory layout of a real
			// compiled implementation.
			//
			// To at least preserve type-safety, we'll
			// just return the zero value of the
			// destination type.
			return zero(t_dst)
		}

		// Conversions between complex numeric types?
		if ut_src.Info()&types.IsComplex != 0 {
			switch ut_dst.(*types.Basic).Kind() {
			case types.Complex64:
				return complex64(x.(complex128))
			case types.Complex128:
				return x.(complex128)
			}
			break // fail: no other conversions for complex
		}

		// Conversions between non-complex numeric types?
		if ut_src.Info()&types.IsNumeric != 0 {
			kind := ut_dst.(*types.Basic).Kind()
			switch x := x.(type) {
			case int64: // signed integer -> numeric?
				switch kind {
				case types.Int:
					return int(x)
				case types.Int8:
					return int8(x)
				case types.Int16:
					return int16(x)
				case types.Int32:
					return int32(x)
				case types.Int64:
					return int64(x)
				case types.Uint:
					return uint(x)
				case types.Uint8:
					return uint8(x)
				case types.Uint16:
					return uint16(x)
				case types.Uint32:
					return uint32(x)
				case types.Uint64:
					return uint64(x)
				case types.Uintptr:
					return uintptr(x)
				case types.Float32:
					return float32(x)
				case types.Float64:
					return float64(x)
				}

			case uint64: // unsigned integer -> numeric?
				switch kind {
				case types.Int:
					return int(x)
				case types.Int8:
					return int8(x)
				case types.Int16:
					return int16(x)
				case types.Int32:
					return int32(x)
				case types.Int64:
					return int64(x)
				case types.Uint:
					return uint(x)
				case types.Uint8:
					return uint8(x)
				case types.Uint16:
					return uint16(x)
				case types.Uint32:
					return uint32(x)
				case types.Uint64:
					return uint64(x)
				case types.Uintptr:
					return uintptr(x)
				case types.Float32:
					return float32(x)
				case types.Float64:
					return float64(x)
				}

			case float64: // floating point -> numeric?
				switch kind {
				case types.Int:
					return int(x)
				case types.Int8:
					return int8(x)
				case types.Int16:
					return int16(x)
				case types.Int32:
					return int32(x)
				case types.Int64:
					return int64(x)
				case types.Uint:
					return uint(x)
				case types.Uint8:
					return uint8(x)
				case types.Uint16:
					return uint16(x)
				case types.Uint32:
					return uint32(x)
				case types.Uint64:
					return uint64(x)
				case types.Uintptr:
					return uintptr(x)
				case types.Float32:
					return float32(x)
				case types.Float64:
					return float64(x)
				}
			}
		}
	}

	panic(fmt.Sprintf("unsupported conversion: %s  -> %s, dynamic type %T", t_src, t_dst, x))
}