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The identity metafunction. Returns X unchanged.
#include <boost/mpl/identity.hpp>
| Parameter | Requirement | Description | 
|---|---|---|
| X | Any type | An argument to be returned. | 
For an arbitrary type x:
typedef identity<x>::type r;
| Return type: | A type. | 
|---|---|
| Semantics: | Equivalent to typedef x r; | 
| Postcondition: | is_same<r,x>::value == true. | 
typedef apply< identity<_1>, char >::type t1; typedef apply< identity<_2>, char,int >::type t2; BOOST_MPL_ASSERT(( is_same< t1, char > )); BOOST_MPL_ASSERT(( is_same< t2, int > ));