When should I use typedef in C++?
c++, typedef
Solution
Template Metaprogramming
`typedef` is necessary for many template metaprogramming tasks -- whenever a class is treated as a "compile-time type function", a `typedef` is used as a "compile-time type value" to obtain the resulting type. E.g. consider a simple metafunction for converting a pointer type to its base type:
template<typename T>
struct strip_pointer_from;
template<typename T>
struct strip_pointer_from<T*> { // Partial specialisation for pointer types
typedef T type;
};
Example: the type expression `strip_pointer_from<double*>::type` evaluates to `double`. Note that template metaprogramming is not commonly used outside of library development.
Simplifying Function Pointer Types
`typedef` is helpful for giving a short, sharp alias to complicated function pointer types:
typedef int (*my_callback_function_type)(int, double, std::string);
void RegisterCallback(my_callback_function_type fn) {
...
}
Problem
In my years of C++ (MFC) programming in I never felt the need to use `typedef`, so I don't really know what is it used for. Where should I use it? Are there any real situations where the use of `typedef` is preferred? Or is this really more a C-specific keyword?