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< title > The MPL Reference Manual: Metafunction Class</ title >
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< table class = "header" >< tr class = "header" >< td class = "header-group navigation-bar" >< span class = "navigation-group" >< a href = "./metafunction.html" class = "navigation-link" > Prev</ a > < a href = "./lambda-expression.html" class = "navigation-link" > Next</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./metafunction.html" class = "navigation-link" > Back</ a > < a href = "./lambda-expression.html" class = "navigation-link" > Along</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./metafunctions-concepts.html" class = "navigation-link" > Up</ a > < a href = "../refmanual.html" class = "navigation-link" > Home</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./refmanual_toc.html" class = "navigation-link" > Full TOC</ a ></ span ></ td >
< td class = "header-group page-location" >< a href = "../refmanual.html" class = "navigation-link" > Front Page</ a > / < a href = "./metafunctions.html" class = "navigation-link" > Metafunctions</ a > / < a href = "./metafunctions-concepts.html" class = "navigation-link" > Concepts</ a > / < a href = "./metafunction-class.html" class = "navigation-link" > Metafunction Class</ a ></ td >
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< div class = "section" id = "metafunction-class" >
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< h1 >< a class = "toc-backref" href = "./metafunctions-concepts.html#id1513" > Metafunction Class</ a ></ h1 >
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< div class = "section" id = "summary" >
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< h3 > Summary</ h3 >
< p > A < em > metafunction class</ em > is a certain form of metafunction representation
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that enables higher-order metaprogramming. More precisely, it's a class
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with a publicly-accessible nested < a class = "reference internal" href = "./metafunction.html" > Metafunction</ a > called < tt class = "literal" >< span class = "pre" >< a href = "./apply.html" class = "identifier" > apply</ a ></ span ></ tt > .
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Correspondingly, a metafunction class invocation is defined as invocation
of its nested < tt class = "literal" >< span class = "pre" >< a href = "./apply.html" class = "identifier" > apply</ a ></ span ></ tt > metafunction.</ p >
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< div class = "section" id = "id827" >
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< h3 >< a class = "subsection-title" href = "#expression-requirements" name = "expression-requirements" > Expression requirements</ a ></ h3 >
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< p > In the following table and subsequent specifications, < tt class = "literal" >< span class = "pre" > f</ span ></ tt > is a < a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > .</ p >
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< tr >< th class = "head" > Expression</ th >
< th class = "head" > Type</ th >
< th class = "head" > Complexity</ th >
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</ tr >
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< tr >< td >< tt class = "literal" >< span class = "pre" > f::< a href = "./apply.html" class = "identifier" > apply</ a > ::type</ span ></ tt ></ td >
< td > Any type</ td >
< td > Unspecified.</ td >
</ tr >
< tr >< td >< tt class = "literal" >< span class = "pre" > f::< a href = "./apply.html" class = "identifier" > apply</ a > <> ::type</ span ></ tt ></ td >
< td > Any type</ td >
< td > Unspecified.</ td >
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< tr >< td >< tt class = "literal" >< span class = "pre" > f::< a href = "./apply.html" class = "identifier" > apply</ a > < a1,...an> ::type</ span ></ tt ></ td >
< td > Any type</ td >
< td > Unspecified.</ td >
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< div class = "section" id = "id828" >
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< h3 >< a class = "subsection-title" href = "#expression-semantics" name = "expression-semantics" > Expression semantics</ a ></ h3 >
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typedef f::< a href = "./apply.html" class = "identifier" > apply</ a > ::type x;
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< tr class = "field" >< th class = "field-name" > Precondition:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > f</ span ></ tt > is a nullary < a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > ; < tt class = "literal" >< span class = "pre" > f::< a href = "./apply.html" class = "identifier" > apply</ a > ::type</ span ></ tt > is a < em > type-name</ em > .</ td >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > x</ span ></ tt > is the result of the metafunction class invocation.</ td >
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typedef f::< a href = "./apply.html" class = "identifier" > apply</ a > <> ::type x;
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< tr class = "field" >< th class = "field-name" > Precondition:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > f</ span ></ tt > is a nullary < a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > ; < tt class = "literal" >< span class = "pre" > f::< a href = "./apply.html" class = "identifier" > apply</ a > <> ::type</ span ></ tt > is a < em > type-name</ em > .</ td >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > x</ span ></ tt > is the result of the metafunction class invocation.</ td >
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typedef f::< a href = "./apply.html" class = "identifier" > apply</ a > < a1,< em > ...</ em > a< em > n</ em > > ::type x;
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< tr class = "field" >< th class = "field-name" > Precondition:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > f</ span ></ tt > is an < em > n</ em > -ary metafunction class; < tt class = "literal" >< span class = "pre" >< a href = "./apply.html" class = "identifier" > apply</ a ></ span ></ tt > is a < a class = "reference internal" href = "./metafunction.html" > Metafunction</ a > .</ td >
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</ tr >
< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< tt class = "literal" >< span class = "pre" > x</ span ></ tt > is the result of the metafunction class
invocation with the actual arguments < tt class = "literal" >< span class = "pre" > a1</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > an</ span ></ tt > .</ td >
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< div class = "section" id = "id829" >
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< h3 >< a class = "subsection-title" href = "#models" name = "models" > Models</ a ></ h3 >
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< li >< a class = "reference internal" href = "./always.html" > always</ a ></ li >
< li >< a class = "reference internal" href = "./arg.html" > arg</ a ></ li >
< li >< a class = "reference internal" href = "./quote.html" > quote</ a ></ li >
< li >< a class = "reference internal" href = "./numeric-cast.html" > numeric_cast</ a ></ li >
< li >< a class = "reference internal" href = "./unpack-args.html" > unpack_args</ a ></ li >
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</ ul >
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< div class = "section" id = "id830" >
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< h3 >< a class = "subsection-title" href = "#see-also" name = "see-also" > See also</ a ></ h3 >
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< p >< a class = "reference internal" href = "./metafunctions.html" > Metafunctions</ a > , < a class = "reference internal" href = "./metafunction.html" > Metafunction</ a > , < a class = "reference internal" href = "./lambda-expression.html" > Lambda Expression</ a > , < a class = "reference internal" href = "./invocation.html" > invocation</ a > , < a class = "reference internal" href = "./apply-wrap.html" > apply_wrap</ a > , < a class = "reference internal" href = "./bind.html" > bind</ a > , < a class = "reference internal" href = "./quote.html" > quote</ a ></ p >
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<!-- Metafunctions/Concepts//Lambda Expression |30 -->
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< td >< div class = "copyright-footer" >< div class = "copyright" > Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</ div >
Distributed under the Boost Software License, Version 1.0. (See accompanying
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