C++11: Perfect forwarding

Consider this function template invoke that invokes the function/functor/lambda expression passed as argument passing it the two extra arguments given:

#include <iostream>
#include <string>

using namespace std;

void sum(int a, int b)
{
    cout << a + b << endl;
}

void concat(const string& a, const string& b)
{
    cout << a + b << endl;
}

template <typename PROC, typename A, typename B>
void invoke(PROC p, const A& a, const B& b)
{
    p(a, b);
}

int main()
{
    invoke(sum, 10, 20);
    invoke(concat, "Hello ", "world");
    return 0;
}

Nice, it works as expected and the result is:

30
Hello world

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C++11: std::future and std::async

C++11 introduces support for asynchronous calls in a very easy way.

An asynchronous call is a method invocation that will be executed in a separate thread (or core or processor); so, the caller of the method does not wait for the result of the execution and continue doing what is next; in this way, the compiler/processor/operating system can optimise the execution of the program and execute several routines at the same time (given the now common multicore systems we all have at home and in our pockets!). The standard library provides the mechanisms to perform those asynchronous calls and store the results until the caller will actually need them.

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C++11: std::thread

The standard library that ships with the new C++11 contains a set of classes to use threads. Before this, we needed to use the OS specific thread facilities each OS provides making our programs hard to port to other platforms.

Anyway, as today (November 16th, 2012), I tried threads using g++ 4.7 in Linux, Windows (through mingw), Mac and NetBSD and I just had success in Linux, Windows and Mac do not implement the thread features and NetBSD misses some details on the implementation (the this_thread::sleep_for() method, for example). Microsoft Visual Studio 2012 ships with good thread support.

To define a thread, we need to use the template class std::thread and we need to pass it a function pointer, a lambda expression or a functor. Look at this example:

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