template with bool parameter

Question

I need to implement template with bool parameter. If bool=true, we need to use list container else we need to use vector container.

template <bool isList> 

How can I do it?

Answer 1

You have at least three ways to do it.

i. Use std::conditional:

template <bool isList> struct A {     typename std::conditional<isList,                                std::list<int>,                               std::vector<int>>::type container; }; 

ii. Use template specialization for the bool parameter

template <bool isList> struct A;  template<> struct A<true> {     std::list<int> container; };  template<> struct A<false> {     std::vector<int> container; }; 

then

A<true>  a1; // container of a1 is a list A<false> a2; // container of a2 is a vector 

iii. Use template functions

If you need a template function type, then you can do it like below. It returns a container based on the entry parameter.

template <bool isList> auto func() -> typename std::conditional<isList,                                           std::list<int>,                                          std::vector<int>>::type {     typename std::result_of<decltype(func<isList>)&()>::type result;      // ...      return result; }; 

then

auto f1 = func<true>();  // f1 is a list auto f2 = func<false>(); // f2 is a vector