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c++templatestypename

How do you decide on value vs reference for template methods

If I have a template function like

template<typename T>
void doSomething(const T arg) {.....}

then I do not know ahead of time if T is a simple int or if it is a huge struct. If it is an int, passing by value makes sense, while the struct should be passed by reference.

How do I design a template function which works sensibly with both types of argument?

Solution

  • The boost::call_traits library has several helpers for stuff like this. In particular, call_traits<T>::param_type

    Defines a type that represents the "best" way to pass a parameter of type T to a function.

    You use it like so:

    template<typename T>
void doSomething(typename boost::call_traits<T>::param_type arg) {.....}

    It basically works by specializing the class for speacial cases. So, e.g., your int case from the question is (indirectly) specialized to int (and not int &).