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# empty.hpp File Reference

## Defines
#define | BOOST_PREPROCESSOR_EMPTY()
| Expands to nothing. Used with BOOST_PREPROCESSOR_IF() and as an unused parameter. More...

## Detailed Description

Click here to see the header.

## Define Documentation

#define BOOST_PREPROCESSOR_EMPTY | (
|  | ) |

| Expands to nothing. Used with BOOST_PREPROCESSOR_IF() and as an unused parameter. Example usage as the implementation of BOOST_PREPROCESSOR_COMMA_IF(C):

      #define BOOST_PREPROCESSOR_COMMA_IF(C)\
        BOOST_PREPROCESSOR_IF(C,BOOST_PREPROCESSOR_COMMA,BOOST_PREPROCESSOR_EMPTY)()
Example usage as an unused macro parameter:

      #define BOOST_PREPROCESSOR_DEF(CV)\
        template<class base>            \
        CV typename implement_subscript_using_begin_subscript<base>::value_type&\
          implement_subscript_using_begin_subscript<base>::operator[]\
          ( index_type                  \
              i                         \
          ) CV                          \
        { return base::begin()[i];      \
        }

      BOOST_PREPROCESSOR_DEF(BOOST_PREPROCESSOR_EMPTY())
      BOOST_PREPROCESSOR_DEF(const)
      #undef BOOST_PREPROCESSOR_DEF
The above expands to:

      template<class base>
      typename implement_subscript_using_begin_subscript<base>::value_type&
        implement_subscript_using_begin_subscript<base>::operator[]
        ( index_type
            i
        )
      { return base::begin()[i];
      }

      template<class base>
      const typename implement_subscript_using_begin_subscript<base>::value_type&
        implement_subscript_using_begin_subscript<base>::operator[]
        ( index_type
            i
        ) const
      { return base::begin()[i];
      }
In case you wonder, the above code is part of a generalized layer for implementing the subscripting operators of a random access container.

© Copyright Housemarque, Inc. 2001

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Generated: 25 Nov 2001