source: downloads/boost_1_34_1/libs/functional/hash/doc/disable.qbk @ 29

[/ Copyright 2005-2006 Daniel James.
 / Distributed under 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:disable Disabling The Extensions]

While [classref boost::hash]'s extensions are generally useful, you might want
to turn them of in order to check that your code will work with other
implementations of TR1. To do this define the macro `BOOST_HASH_NO_EXTENSIONS`.
When this macro is defined, only the specialisations detailed
in TR1 will be declared. But, if you later undefine the macro and include
<[headerref boost/functional/hash.hpp]> then the non-specialised form will be defined
- activating the extensions.

It is strongly recommended that you never undefine the macro - and only define
it so that it applies to the complete translation unit, either by defining it
at the beginning of the main source file or, preferably, by using a compiler
switch or preference. And you really should never define it in header files.

If you are writing a library which has code in the header which requires the
extensions, then the best action is to tell users not to define the macro.
Their code won't ['require] the macro.

Translation units that are compiled with the macro defined will link with units
that were compiled without it. This feature has been designed to avoid ODR
violations.

[endsect]