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Placeholder Expression

Description

A Placeholder Expression is a type that is either a placeholder or a class template specialization with at least one argument that itself is a Placeholder Expression.

Expression requirements

If X is a class template, and a1,... an are arbitrary types, then X<a1,...,an> is a Placeholder Expression if and only if all of the following conditions hold:

• At least one of the template arguments a1,... an is a placeholder or a Placeholder Expression.
• All of X's template parameters, including the default ones, are types.
• The number of X's template parameters, including the default ones, is less or equal to the value of BOOST_MPL_LIMIT_METAFUNCTION_ARITYconfiguration macro.

Models

• _1
• plus<_, int_<2> >
• if_< less<_1, int_<7> >, plus<_1,_2>, _1 >

See also

Lambda Expression, Placeholders, Metafunctions, apply, lambda

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Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams 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) |