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The TR1 Tuple interface is specified to provide uniform access to std::pair as if it were a 2 element tuple.

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.