How to add element to various container depending of type using template

Question

I\'ve got rather silly question but I hope that you can help me with that.

I\'ve got class with multiple vectors, and this vectors have different storage types.

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Answer 1

Instead of having

template   void addElement(T Obj);

Just overload the function instead. That would give you

void addElement(const B& Obj)
{
    V1.push_back({Obj.Name, Obj});
}

void addElement(const C& Obj)
{
    V2.push_back({Obj.Name, Obj});
}

This saves you all the syntax of specializing the template or needing C++17 and if constexpr to make the decision at compile time.

---

The reason

template   void addElement(T Obj){
std::pair AddedPair(Obj.Name, Obj);

    if (typeid(T) == typeid(B)) 
        V1.push_back(AddedPair);

    if (typeid(T) == typeid(C)) 
        V2.push_back(AddedPair);

}

Doesn't work is the code in each if block needs to be valid (even if it could never be reached), but it can't be because you would be adding a different type into the vectors. if constexpr helps but I find overloading is just as much typing and makes the code non-backwards compatible.

That means you would either have to specialize the template like

template   void addElement(T Obj);

template <>  void addElement(B Obj)
{
    V1.push_back({Obj.Name, Obj});
}   
template <>  void addElement(C Obj)
{
    V1.push_back({Obj.Name, Obj});
}

or using if constexpr:

template   void addElement(T Obj){
std::pair AddedPair(Obj.Name, Obj);

    if constexpr(std::is_same_v) 
        V1.push_back(AddedPair);

    if constexpr(std::is_same_v) 
        V2.push_back(AddedPair);

}