Playing with C++0x -- tuple

C++0x is approaching, and it comes with a lot of new stuff, so I've decided to play with it.

Some C++0x features are already available in g++ 4.3. Others will be available in the 4.4 release -- see this page for a summary of C++0x language support in g++.

What is a tuple? It's a std::pair on steroïds: it can contain any number of elements. For the impatient, the whole sample program is available from here. It can be compiled with:
g++-4.3 --std=c++0x tuple.cpp -o tuple.

Now let's see how to create a tuple:

#include <string>
#include <tuple>

typedef std::tuple<int, double, std::string> my_tuple_t;
my_tuple_t a_tuple(1, 5.0);

Every element of the tuple gets initialized to its default value if it's not specified. Indeed displaying the third element:

std::cout << std::get<2>(a_tuple) << std::endl;

outputs nothing, because the string element was default-constructed to an empty string. The std::make_tuple function, like std::make_pair for std::pair, can be used to create a tuple using type deduction:

std::cout << std::get<1>(std::make_tuple(false, std::string("see"))) << std::endl;

A tuple element can be changed using the same get function:

std::get<2>(a_tuple) = "a string";

Of course, a tuple is type safe. Trying to put a string at the first element:

std::get<0>(a_tuple) = "another string";

does not compile. But there's more: you also get a compilation error when trying to access an element that does not exist. For example trying to display fourth element does not compile:

std::cout << std::get<3>(a_tuple) << std::endl;

What else can you do with tuples? You can test them for equality, or assign them:

my_tuple_t another_tuple = std::make_tuple(2, 10.0, std::string("nothing"));
std::cout << (a_tuple == another_tuple) << std::endl;
another_tuple = a_tuple;
std::cout << (a_tuple == another_tuple) << std::endl;

You can also retrieve multiple elements at once, possibly ignoring some of them:

std::string a_string;
std::tie(std::ignore, std::ignore, a_string) = another_tuple;

Last, you can concatenate two tuples into a new tuple:

std::tuple<int, double, std::string, bool, std::string> cat =
    std::tuple_cat(a_tuple, std::make_tuple(false, std::string("see")));