Cleanest way for conditional code instantiation in C++ template

Question

I\'m trying to get the following C++ code running:

#include 

template class ConditionalData {
};

template 

        

Answer 1

First of all, you don't require 3 versions of class ConditionalData, because bool can be either true or false. So let me simplify it as following:

template class ConditionalData {
};                 //^^^^^^^^^^^^

template  class ConditionalData {
private:
    T data;
public:
    void setData(T _data) { data = _data; }
};

Secondly, to answer your question: Whichever members are falling for false category, just overload them outside the class body as following:

template class A { 
public:
    A() {
        ConditionalData data;
        if (hasdata) {
            data.setData(3);
        }
    }   
};

template<> A::A() {}  // Does nothing for `false` condition