func (f *exprFlags) SetAddressable()     { *f |= 32 }
func (f *exprFlags) SetAssignable()      { *f |= 64 }
func (f *exprFlags) SetHasOk()           { *f |= 128 }
func (f *exprFlags) SetIsRuntimeHelper() { *f |= 256 }

// a typeAndValue contains the results of typechecking an expression.
// It is embedded in expression nodes.
type typeAndValue struct {
	tv TypeAndValue
}

func runtimeSym(info *types2.Info, name string) *syntax.Name {
	obj := runtimePkg.Scope().Lookup(name)
	n := syntax.NewName(nopos, "runtime."+name)
	tv := syntax.TypeAndValue{Type: obj.Type()}
	tv.SetIsValue()
	tv.SetIsRuntimeHelper()
	n.SetTypeInfo(tv)
	info.Uses[n] = obj
	return n
}

// setPos walks the top structure of x that has no position assigned
// and assigns it all to have position pos.