Re: template & no matching function for call to

[burlen <burlen.loring@xxxxxxxxx>]

of course, thanks

Brian Budge wrote:
> Access is defined for a ref, but a const ref is required because the
> calling member function of Value<int> is const (and so it's data must
> be const protected).
>
>   Brian
>
> On Mon, Feb 22, 2010 at 5:45 PM, burlen <burlen.loring@xxxxxxxxx> wrote:
>   
> > Hi,
> >
> > I'm getting the error that gcc cannot match my templated member function
> > call. I'm not seeing where the ambiguity lies, can someone explain why g++
> > doesn't find it?
> >
> > Here are the error
> >
> > $g++ minimal.cpp
> > minimal.cpp: In member function ‘T Value<T>::GetValue() const [with T =
> > int]’:
> > minimal.cpp:59: instantiated from here
> > minimal.cpp:46: error: no matching function for call to
> > ‘ValueTraits<int>::Access(const ValueUnion&) const’
> > minimal.cpp:24: note: candidates are: int
> > ValueTraits<int>::Access(ValueUnion&) const
> >
> >
> > Here is the code from minimal.cpp:
> >
> > #include <iostream>
> > using std::cerr;
> > using std::endl;
> >
> > //=============================================================================
> > typedef union
> > {
> > int Int;
> > double Double;
> > }
> > ValueUnion;
> >
> > //=============================================================================
> > template <typename T>
> > class ValueTraits {};
> >
> > //=============================================================================
> > template<>
> > class ValueTraits<int>
> > {
> > public:
> > int Access(ValueUnion &vu) const { return vu.Int; }
> > void Assign(ValueUnion &vu, int val){ vu.Int=val; }
> > };
> >
> > //=============================================================================
> > template<>
> > class ValueTraits<double>
> > {
> > public:
> > double Access(ValueUnion &vu) const { return vu.Double; }
> > void Assign(ValueUnion &vu, double val){ vu.Double=val; }
> > };
> >
> > //=============================================================================
> > template<typename T>
> > class Value
> > {
> > public:
> > virtual T GetValue() const { return this->Traits.Access(this->Data); }
> > virtual void SetValue(T data) { this->Traits.Assign(this->Data,data); }
> >
> > private:
> > ValueTraits<T> Traits;
> > ValueUnion Data;
> > };
> >
> > //-----------------------------------------------------------------------------
> > int main(int argc, char **ragv)
> > {
> > Value<int> iv;
> > iv.SetValue(2);
> > cerr << "iv=" << iv.GetValue() << endl;
> >
> > Value<double> dv;
> > dv.SetValue(2.2);
> > cerr << "dv=" << dv.GetValue() << endl;
> >
> > return 0;
> > }
> >
> >
> >
> >