A variable (or an attribute) can be equal to a type?

Question

I wanted to know if a variable can be equal to a type (here it's the magic_type)

#include <typeinfo>

template<typename T>
class C
{
public:
   magic_type t;
   t list;
   T data;

   C(void)
   {
      if (typeid(data) == typeid(int))
         t = float; // so typeid(list) = typedid(float)
      else
         t = int; // and typeid(list) = typedid(int)
   }
};

Answer 1

If you want the magic_type be float when T == int and otherwise float, use std::conditional_t. This will resolve the magic_type at compile time.

In order to check whether two types are the same, you could use std::is_same_v. Include <type_traits>, for both of the trait's usage.

#include <type_traits>  // std::conditional_t, std::is_same_v

template<typename T>
class C
{
   // type alias
   using magic_type = std::conditional_t<std::is_same_v<T, int>, float, int>;

   magic_type t;  // now `magic_type` == `float` if `T` == `int`, otherwise `float`
   T data;

public:       
   // ... code
};