enable_if in the Boost library is a very powerful and practical tool that also plays an important role in C++ template metaprogramming

enable_if in the Boost library is a very powerful and practical tool that also plays an important role in C++ template metaprogramming. In order to better understand and use this library, we need to write some test programs to verify its functionality and performance.

Here is a simple example:

#include <iostream>
#include <type_traits>
#include <boost/utility/enable_if.hpp>

template<class T>
typename boost::enable_if<std::is_integral<T>, T>::type
add(T x, T y)
{
  std::cout << "Adding two integers: ";
  return x + y;
}

template<class T>
typename boost::disable_if<std::is_integral<T>, T>::type
add(T x, T y)
{
  std::cout << "Adding two non-integers: ";
  return x + y;
}

int main()
{
  int a = 1, b = 2;
  float c = 1.2, d = 3.4;

  std::cout << add(a, b) << std::endl;
  std::cout << add(c, d) << std::endl;

  return 0;
}

In this example, we define two function templates add, which are used to handle the addition operation of two integers or two non-integers respectively. Using enable_if can make type checking more strict, only when the input parameter type meets our requirements, a specific function will be enabled