Why Can\'t My Function Handle Multiple Container Types Using `std::is_same`?

Why Your Function Can't Handle Multiple Container Types Using std::is_same

Your intention is to create a generic function, print_container, that can print the elements of both stack and queue containers. However, despite using std::is_same to check the container type, your function encounters errors.

Cause of Errors:

The errors arise because both branches of the if-else statement must be compilable. In your case, when Cont is std::stack, the front member function is accessed, which doesn't exist in std::stack. Similarly, when Cont is std::queue, the top member function is accessed, which doesn't exist in std::queue.

Partial Specialization Solution:

One possible solution is to use partial specialization to handle each container type separately:

<br>template <typename Cont><br>struct element_accessor;</p>
<p>template <typename T><br>struct element_accessor<std::stack<T>> {<br>   const T& operator()(const std::stack<T>& s) const { return s.top(); }<br>};</p>
<p>template <typename T><br>struct element_accessor<std::queue<T>> {<br>   const T& operator()(const std::queue<T>& q) const { return q.front(); }<br>};</p>
<p>template<typename Cont><br>void print_container(Cont& cont){<br>   while(!cont.empty()){</p>
<pre class="brush:php;toolbar:false">  auto elem = element_accessor<Cont>{}(cont);
  std::cout << elem << '\n';
  cont.pop();

}
}

This approach delegates the retrieval of elements to specialized element_accessor functions, which provide the correct accessor for each container type.

C 17 Solution with if constexpr:

If you're using C 17 or later, you can also leverage the if constexpr construct:

<br>template<template<class> typename Cont, typename T><br>void print_container(Cont<T>& cont){<br>   while(!cont.empty()){</p><pre class="brush:php;toolbar:false">  if constexpr (std::is_same_v<Cont<T>, std::stack<T>>) 
     std::cout << cont.top() << '\n';
  else if constexpr (std::is_same_v<Cont<T>, std::queue<T>>) 
     std::cout << cont.front() << '\n';
  cont.pop();

}
}

This solution uses if constexpr to conditionally execute the appropriate code based on the container type, avoiding the need for partial specialization.

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