[/==============================================================================
    Copyright (C) 2001-2007 Joel de Guzman, Dan Marsden, Tobias Schwinger

    Use, modification and distribution is subject to the Boost Software
    License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
    http://www.boost.org/LICENSE_1_0.txt)
===============================================================================/]
[section Tuple]

The TR1 technical report describes extensions to the C++ standard library.
Many of these extensions will be considered for the next
iteration of the C++ standard. TR1 describes a tuple type, and
support for treating `std::pair` as a type of tuple.

Fusion provides full support for the __tr1__tuple__ interface, and the extended
uses of `std::pair` described in the TR1 document.

[section Class template tuple]
Fusion's implementation of the __tr1__tuple__ is also a fusion __forward_sequence__.
As such the fusion tuple type provides a lot of functionality beyond that required by TR1.

Currently tuple is basically a synonym for __vector__, although this may be changed
in future releases of fusion.

[heading Synopsis]
    template<
        typename T1 = __unspecified__,
        typename T2 = __unspecified__,
        ...
        typename TN = __unspecified__>
    class tuple;

/tuple.hpp>

[section Construction]

[heading Description]
The __tr1__tuple__ type provides a default constructor, a constructor that takes initializers for all of its elements, a copy constructor, and a converting copy constructor. The details of the various constructors are described in this section.

[heading Specification]

[variablelist Notation
    [[`T1 ... TN`, `U1 ... UN`][Tuple element types]]
    [[`P1 ... PN`]             [Parameter types]]
    [[`Ti`, `Ui`]              [The type of the `i`th element of a tuple]]
    [[`Pi`]                    [The type of the `i`th parameter]]
]

    tuple();

[*Requirements]: Each `Ti` is default constructable.

[*Semantics]: Default initializes each element of the tuple.

    tuple(P1,P2,...,PN);

[*Requirements]: Each `Pi` is `Ti` if `Ti` is a reference type, `const Ti&` otherwise.

[*Semantics]: Copy initializes each element with the corresponding parameter.

    tuple(const tuple& t);

[*Requirements]: Each `Ti` should be copy constructable.

[*Semantics]: Copy constructs each element of `*this` with the corresponding element of `t`.

    template<typename U1, typename U2, ..., typename UN>
    tuple(const tuple<U1, U2, ..., UN>& t);

[*Requirements]: Each `Ti` shall be constructible from the corresponding `Ui`.

[*Semantics]: Constructs each element of `*this` with the corresponding element of `t`.

[endsect]

[section Tuple creation functions]

[heading Description]
TR1 describes 2 utility functions for creating __tr1__tuple__s. `make_tuple` builds a tuple out of it's argument list, and `tie` builds a tuple of references to it's arguments. The details of these creation functions are described in this section.

[heading Specification]

    template<typename T1, typename T2, ..., typename TN>
    tuple<V1, V2, ..., VN> make_tuple(const T1& t1, const T2& t2, ..., const TN& tn);

Where `Vi` is `X&` if the cv-unqualified type `Ti` is `reference_wrapper<X>`, otherwise `Vi` is `Ti`.

[*Returns]: `tuple<V1, V2, ..., VN>(t1, t2, ..., tN)`

    template<typename T1, typename T2, ..., typename TN>
    tuple<T1&, T2&, ..., TN&> tie(T1& t1, T2& t2, ..., TN& tn);

[*Returns]: tuple<T1&, T2&, ..., TN&>(t1, t2, ..., tN). When argument `ti` is `ignore`, assigning any value to the corresponding tuple element has has no effect.

[endsect]

[section Tuple helper classes]

[heading Description]
The __tr1__tuple__ provides 2 helper traits, for compile time access to the tuple size, and the element types.

[heading Specification]

    tuple_size<T>::value

[*Requires]: `T` is any fusion sequence type, including `tuple`.

[*Type]: __mpl_integral_constant__

[*Value]: The number of elements in the sequence. Equivalent to `__result_of_size__<T>::type`.

    tuple_element<I, T>::type

[*Requires]: `T` is any fusion sequence type, including `tuple`. `0 <= I < N` or the program is ill formed.

[*Value]: The type of the `I`th element of `T`. Equivalent to `__result_of_value_at__<I,T>::type`.

[endsect]

[section Element access]

[heading Description]
The __tr1__tuple__ provides the `get` function to provide access to it's elements by zero based numeric index.

[heading Specification]
    template<int I, T>
    RJ get(T& t);

[*Requires]: `0 < I <= N`. The program is ill formed if `I` is out of bounds.
`T` is any fusion sequence type, including `tuple`.

[*Return type]: `RJ` is equivalent to `__result_of_at_c__<I,T>::type`.

[*Returns]: A reference to the `I`th element of `T`.

    template<int I, typename T>
    PJ get(T const& t);

[*Requires]: `0 < I <= N`. The program is ill formed if `I` is out of bounds.
`T` is any fusion sequence type, including `tuple`.

[*Return type]: `PJ` is equivalent to `__result_of_at_c__<I,T>::type`.

[*Returns]: A const reference to the `I`th element of `T`.

[endsect]

[section Relational operators]

[heading Description]
The __tr1__tuple__ provides the standard boolean relational operators.

[heading Specification]

[variablelist Notation
    [[`T1 ... TN`, `U1 ... UN`][Tuple element types]]
    [[`P1 ... PN`]             [Parameter types]]
    [[`Ti`, `Ui`]              [The type of the `i`th element of a tuple]]
    [[`Pi`]                    [The type of the `i`th parameter]]
]

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator==(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(lhs) == __tuple_get__<i>(rhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns `true` if and only if `__tuple_get__<i>(lhs) == __tuple_get__<i>(rhs)` for all `i`.
For any 2 zero length tuples `e` and `f`, `e == f` returns `true`.

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator<(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(lhs) < __tuple_get__<i>(rhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns the lexicographical comparison of between `lhs` and `rhs`.

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator!=(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(lhs) == __tuple_get__<i>(rhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns `!(lhs == rhs)`.

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator<=(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(rhs) < __tuple_get__<i>(lhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns `!(rhs < lhs)`

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator>(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(rhs) < __tuple_get__<i>(lhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns `rhs < lhs`.

    template<typename T1, typename T2, ..., typename TN,
             typename U1, typename U2, ..., typename UN>
    bool operator>=(
        const tuple<T1, T2, ..., TN>& lhs,
        const tuple<U1, U2, ..., UN>& rhs);

[*Requirements]: For all `i`, `1 <= i < N`, `__tuple_get__<i>(lhs) < __tuple_get__<i>(rhs)` is a valid
expression returning a type that is convertible to `bool`.

[*Semantics]: Returns `!(lhs < rhs)`.

[endsect]

[endsect]

[section Pairs]

[heading Description]
The __tr1__tuple__ interface is specified to provide uniform access to `std::pair` as if it were a 2 element tuple.

[heading Specification]

    tuple_size<std::pair<T1, T2> >::value

[*Type]: An __mpl_integral_constant__

[*Value]: Returns 2, the number of elements in a pair.

    tuple_element<0, std::pair<T1, T2> >::type

[*Type]: `T1`

[*Value]: Returns the type of the first element of the pair

    tuple_element<1, std::pair<T1, T2> >::type

[*Type]: `T2`

[*Value]: Returns thetype of the second element of the pair

    template<int I, typename T1, typename T2>
    P& get(std::pair<T1, T2>& pr);

    template<int I, typename T1, typename T2>
    const P& get(const std::pair<T1, T2>& pr);

[*Type]: If `I == 0` `P` is `T1`, else if `I == 1` `P` is `T2` else the program is ill-formed.

[*Returns: `pr.first` if `I == 0` else `pr.second`.

[endsect]

[endsect]