template & no matching function for call to

[burlen]

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@gmail.com> 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]Â’:
>> 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;
>> }
>>
>>
>>
>>