async.cpp

#include <future>
#include <iostream>
#include <string>

std::string helloFunction(const std::string &s) {
  return "Hello C++11 from " + s + ".";
}

class HelloFunctionObject {
public:
  std::string operator()(const std::string &s) const {
    std::this_thread::sleep_for(std::chrono::seconds(2));
    return "Hello C++11 from " + s + ".";
  }
};

int main() {

  std::cout << std::endl;

  // 带函数的future
  auto futureFunction = std::async(helloFunction, "function");

  // 带函数对象的future
  HelloFunctionObject helloFunctionObject;
  auto futureFunctionObject =
      std::async(helloFunctionObject, "function object");

  // 带匿名函数的future
  auto futureLambda = std::async(
      [](const std::string &s) { return "Hello C++11 from " + s + "."; },
      "lambda function");

  std::cout << futureFunction.get() << "\n"
            << futureFunctionObject.get() << "\n"
            << futureLambda.get() << std::endl;

  std::cout << std::endl;
}