C++ Template Metaprogramming - Concepts, Tools, and Techniques from Boost and Beyond @Team LiB by By David Abrahams Aleksey Gurtovoy

Author:By David Abrahams, Aleksey Gurtovoy
Language: eng
Format: mobi
ISBN: 0321227255
Publisher: Addison Wesley Professional
Published: 2011-10-03T15:22:49.999109+00:00

BOOST_MPL_ASSERT((bool-valued-nullary-metafunction))

Note that double parentheses are required even if no commas appear in the condition.

Here are the changes we might make to apply this macro in our factorial example:

...

#include <boost/mpl/greater_equal.hpp>

#include <boost/mpl/assert.hpp>

template <class N>

struct factorial

...

{

BOOST_MPL_ASSERT((mpl::greater_equal<N,mpl::int_<0> >));

};

The advantage of BOOST_MPL_ASSERT is that it puts the name of its argument metafunction in the diagnostic. GCC now reports:

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