std::mem_fun_ref(3)

✨ std::mem_fun_ref(3) ✨

okay bestie, this one is from the C++ Standard Library manual, and it’s giving vintage C++ chaos: a template that wraps member functions, expects a reference, got deprecated in C++11, and then got yeeted in C++17. 💅

💖 NAME 💖

std::mem_fun_ref - std::mem_fun_ref

🌸 Synopsis 🌸

Defined in header <functional>

template< class Res, class T >                             (1)
(deprecated in C++11)
(removed in C++17)
std::mem_fun_ref_t<Res,T> mem_fun_ref( Res (T::*f)() );

template< class Res, class T >
(deprecated in C++11)
(removed in C++17)
std::const_mem_fun_ref_t<Res,T> mem_fun_ref( Res (T::*f)() const );

template< class Res, class T, class Arg >
(deprecated in C++11)
(removed in C++17)
std::mem_fun1_ref_t<Res,T,Arg> mem_fun_ref( Res (T::*f)(Arg) );

template< class Res, class T, class Arg >
(deprecated in C++11)
(removed in C++17)
std::const_mem_fun1_ref_t<Res,T,Arg> mem_fun_ref( Res (T::*f)(Arg) const );

Creates a member function wrapper object, deducing the target type from the template arguments. The wrapper object expects a reference to an object of type T as the first parameter to its operator(). ✨

1. Effectively calls std::mem_fun_ref_t<S,T>(f) or std::const_mem_fun_ref_t<S,T>(f).
2. Effectively calls std::mem_fun1_ref_t<S,T>(f) or std::const_mem_fun1_ref_t<S,T>(f).

This function and the related types were deprecated in C++11 and removed in C++17 in favor of the more general std::mem_fn and std::bind, both of which create callable adaptor-compatible function objects from member functions. 🫶

🎀 Parameters 🎀

• f — pointer to a member function to create a wrapper for.

🦋 Return value 🦋

A function object wrapping f.

💜 Exceptions 💜

May throw implementation-defined exceptions.

🌈 Notes 🌈

The difference between std::mem_fun and std::mem_fun_ref is that the former produces a function wrapper that expects a pointer to an object, whereas the latter — a reference. no cap, that’s the whole vibe check 😭

🔥 Example 🔥

Uses std::mem_fun_ref to bind std::string’s member function size().

// Run this code

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>

int main()
{
    std::vector<std::string> v = {"once", "upon", "a", "time"};
    std::transform(v.cbegin(), v.cend(),
                   std::ostream_iterator<std::size_t>(std::cout, " "),
                   std::mem_fun_ref(&std::string::size));
}

⭐ Output ⭐

4 4 1 4

👑 See also 👑

• mem_fun — creates a wrapper from a pointer to member function, callable with a pointer to object (deprecated in C++11) (removed in C++17) (function template).

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mwah 💋 — this page came from the C++ Standard Library manual, sourced from http://cppreference.com, version/date 2024.06.10. bye bestie, go wrap responsibly 🫶