ex1.cpp

/*
    "`for_each_arg` explained and expanded"
    C++Now 2015 Lightning Talk
    - Vittorio Romeo

    http://vittorioromeo.info
    vittorio.romeo@outlook.com
*/

// The files used in this talk are available at:
/*
    https://github.com/SuperV1234/cppnow2015
*/

#include <iostream>

template <typename TF, typename... Ts>
void forArgs(TF&& mFn, Ts&&... mArgs)
{
    // We use an `initializer_list` to create a context
    // where variadic parameter expansion can take place.
    return (void)std::initializer_list<int>{
        // Every element of the `initializer_list` is an
        // expression enclosed in round parenthesis.
        (
            // In the parenthesis, the result of the `mFn`
            // function call is followed by the comma
            // operator and an integer (zero in this
            // case).

            // Thanks to the comma operator, the expression
            // evaluates to an (unused) integer, which is
            // accepted by the `initializer_list`.

            mFn(std::forward<Ts>(mArgs)),

            0)...};
}

/*

// The following `forArgs` call...

forArgs
(
    [](const auto& x){ std::cout << x << " "; },
    "hello",
    1,
    2,
    3
);

// ..roughly expands to...

(void) std::initializer_list<int>
{
    ([](const auto& x){ std::cout << x; }("hello"), 0),
    ([](const auto& x){ std::cout << x; }(1), 0),
    ([](const auto& x){ std::cout << x; }(2), 0),
    ([](const auto& x){ std::cout << x; }(3), 0)
}

// ...which is the same as writing...

std::cout << "hello";
std::cout << 1;
std::cout << 2;
std::cout << 3;

*/

int main()
{
    // Prints "hello 1 2 3".

    forArgs(
        [](const auto& x)
        {
            std::cout << x << " ";
        },
        "hello", 1, 2, 3);

    return 0;
}