C++ Primer Plus

The function Wrapper and Template Inefficiencies

Consider the following line of code:

answer = ef(q);

What is ef? It could be the name of a function. It could be a pointer to a function. It could be a function object. It could be a name assigned to a lambda expression. These all are examples of callable types. The abundance of callable types can lead to template inefficiencies. To see this, let’s examine a simple case.

First, let’s define some templates in a header file, as shown in Listing 18.6.

Listing 18.6. somedefs.h

// somedefs.h#include <iostream>template <typename T, typename F>T use_f(T v, F f){    static int count = 0;    count++;    std::cout << "  use_f count = " << count              << ", &count = " << &count << std::endl;    return ...