generic/call.cpp

The following code example is taken from the book
C++ Move Semantics - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2020
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include "call.hpp"
#include <iostream>
#include <string>

std::string nextString()
{
  return "Let's dance";
}

std::ostream& print(std::ostream& strm, const std::string& val)
{
  return strm << "value: " << val;
}

std::string&& returnArg(std::string&& arg)
{
  return std::move(arg);
}

int main()
{
  auto s = call(nextString);                   // call() returns temporary object

  auto&& ref = call(returnArg, std::move(s));  // call() returns rvalue reference to s
  std::cout << "s:   " << s << '\n';
  std::cout << "ref: " << ref << '\n';

  auto str = std::move(ref);                   // move value from s and ref to str
  std::cout << "s: "   << s << '\n';
  std::cout << "ref: " << ref << '\n';
  std::cout << "str: " << str << '\n';

  call(print, std::cout, str) << '\n';         // call() returns reference to std::cout
}