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< title > The MPL Reference Manual: lambda</ title >
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< body class = "docframe refmanual" >
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< table class = "header" >< tr class = "header" >< td class = "header-group navigation-bar" >< span class = "navigation-group" >< a href = "./placeholders.html" class = "navigation-link" > Prev</ a > < a href = "./bind.html" class = "navigation-link" > Next</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./placeholders.html" class = "navigation-link" > Back</ a > < a href = "./bind.html" class = "navigation-link" > Along</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./composition-and-argument-binding.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 = "./composition-and-argument-binding.html" class = "navigation-link" > Composition and Argument Binding</ a > / < a href = "./lambda.html" class = "navigation-link" > lambda</ a ></ td >
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</ tr ></ table >< div class = "header-separator" ></ div >
< div class = "section" id = "lambda" >
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< h1 >< a class = "toc-backref" href = "./composition-and-argument-binding.html#id1530" > lambda</ a ></ h1 >
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< div class = "section" id = "id922" >
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< h3 >< a class = "subsection-title" href = "#synopsis" name = "synopsis" > Synopsis</ a ></ h3 >
< pre class = "literal-block" >
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template<
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typename X
, typename Tag = < em > unspecified</ em >
>
struct < a href = "./lambda.html" class = "identifier" > lambda</ a >
{
typedef < em > unspecified</ em > type;
};
</ pre >
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< div class = "section" id = "id923" >
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< h3 >< a class = "subsection-title" href = "#description" name = "description" > Description</ a ></ h3 >
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< p > If < tt class = "literal" >< span class = "pre" > X</ span ></ tt > is a < a class = "reference internal" href = "./placeholder-expression.html" > Placeholder Expression</ a > , transforms < tt class = "literal" >< span class = "pre" > X</ span ></ tt > into a corresponding
< a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > , otherwise < tt class = "literal" >< span class = "pre" > X</ span ></ tt > is returned unchanged.</ p >
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</ div >
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< div class = "section" id = "id924" >
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< h3 >< a class = "subsection-title" href = "#header" name = "header" > Header</ a ></ h3 >
< pre class = "literal-block" >
#include < < a href = "../../../../boost/mpl/lambda.hpp" class = "header" > boost/mpl/lambda.hpp</ a > >
</ pre >
</ div >
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< div class = "section" id = "id925" >
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< h3 >< a class = "subsection-title" href = "#parameters" name = "parameters" > Parameters</ a ></ h3 >
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< table border = "1" class = "docutils table" >
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< colgroup >
< col width = "18%" />
< col width = "27%" />
< col width = "55%" />
</ colgroup >
< thead valign = "bottom" >
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< tr >< th class = "head" > Parameter</ th >
< th class = "head" > Requirement</ th >
< th class = "head" > Description</ th >
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</ tr >
</ thead >
< tbody valign = "top" >
< tr >< td >< tt class = "literal" >< span class = "pre" > X</ span ></ tt ></ td >
< td > Any type</ td >
< td > An expression to transform.</ td >
</ tr >
< tr >< td >< tt class = "literal" >< span class = "pre" > Tag</ span ></ tt ></ td >
< td > Any type</ td >
< td > A tag determining transform semantics.</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id926" >
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< h3 >< a class = "subsection-title" href = "#expression-semantics" name = "expression-semantics" > Expression semantics</ a ></ h3 >
< p > For arbitrary types < tt class = "literal" >< span class = "pre" > x</ span ></ tt > and < tt class = "literal" >< span class = "pre" > tag</ span ></ tt > :</ p >
< pre class = "literal-block" >
typedef < a href = "./lambda.html" class = "identifier" > lambda</ a > < x> ::type f;
</ pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Return type:</ th >< td class = "field-body" >< p class = "first" >< a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > .</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< p class = "first" > If < tt class = "literal" >< span class = "pre" > x</ span ></ tt > is a < a class = "reference internal" href = "./placeholder-expression.html" > Placeholder Expression</ a > in a general form < tt class = "literal" >< span class = "pre" > X< a1,...an> </ span ></ tt > , where
< tt class = "literal" >< span class = "pre" > X</ span ></ tt > is a class template and < tt class = "literal" >< span class = "pre" > a1</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > an</ span ></ tt > are arbitrary types, equivalent
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to</ p >
< pre class = "literal-block" >
typedef < a href = "./protect.html" class = "identifier" > protect</ a > < < a href = "./bind.html" class = "identifier" > bind</ a > <
< a href = "./quote.html" class = "identifier" > quote</ a >< em > n</ em > < X>
, < a href = "./lambda.html" class = "identifier" > lambda</ a > < a1> ::type,< em > ...</ em > < a href = "./lambda.html" class = "identifier" > lambda</ a > < a< em > n</ em > > ::type
> > f;
</ pre >
< p class = "last" > otherwise, < tt class = "literal" >< span class = "pre" > f</ span ></ tt > is identical to < tt class = "literal" >< span class = "pre" > x</ span ></ tt > .</ p >
</ td >
</ tr >
</ tbody >
</ table >
<!-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
< pre class = "literal-block" >
typedef < a href = "./lambda.html" class = "identifier" > lambda</ a > < x,tag> ::type f;
</ pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" />
< col class = "field-body" />
< tbody valign = "top" >
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< tr class = "field" >< th class = "field-name" > Return type:</ th >< td class = "field-body" >< p class = "first" >< a class = "reference internal" href = "./metafunction-class.html" > Metafunction Class</ a > .</ p >
</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" >< p class = "first" > If < tt class = "literal" >< span class = "pre" > x</ span ></ tt > is a < a class = "reference internal" href = "./placeholder-expression.html" > Placeholder Expression</ a > in a general form < tt class = "literal" >< span class = "pre" > X< a1,...an> </ span ></ tt > , where
< tt class = "literal" >< span class = "pre" > X</ span ></ tt > is a class template and < tt class = "literal" >< span class = "pre" > a1</ span ></ tt > ,... < tt class = "literal" >< span class = "pre" > an</ span ></ tt > are arbitrary types, equivalent
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to</ p >
< pre class = "literal-block" >
typedef < a href = "./protect.html" class = "identifier" > protect</ a > < < a href = "./bind.html" class = "identifier" > bind</ a > <
< a href = "./quote.html" class = "identifier" > quote</ a >< em > n</ em > < X,tag>
, < a href = "./lambda.html" class = "identifier" > lambda</ a > < a1,tag> ::type,< em > ...</ em > < a href = "./lambda.html" class = "identifier" > lambda</ a > < a< em > n</ em > ,tag> ::type
> > f;
</ pre >
< p class = "last" > otherwise, < tt class = "literal" >< span class = "pre" > f</ span ></ tt > is identical to < tt class = "literal" >< span class = "pre" > x</ span ></ tt > .</ p >
</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id927" >
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< h3 >< a class = "subsection-title" href = "#example" name = "example" > Example</ a ></ h3 >
< pre class = "literal-block" >
template< typename N1, typename N2 > struct int_plus
: < a href = "./int.html" class = "identifier" > int_</ a > < ( N1::value + N2::value )>
{
};
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typedef < a href = "./lambda.html" class = "identifier" > lambda</ a > < int_plus< < a href = "./placeholders.html" class = "identifier" > _1</ a > , < a href = "./int.html" class = "identifier" > int_</ a > < 42> > > ::type f1;
typedef < a href = "./bind.html" class = "identifier" > bind</ a > < < a href = "./quote.html" class = "identifier" > quote</ a >< tt class = "literal" >< span class = "pre" > 2</ span ></ tt > < int_plus> , < a href = "./placeholders.html" class = "identifier" > _1</ a > , < a href = "./int.html" class = "identifier" > int_</ a > < 42> > f2;
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typedef f1::< a href = "./apply.html" class = "identifier" > apply</ a > < 42> ::type r1;
typedef f2::< a href = "./apply.html" class = "identifier" > apply</ a > < 42> ::type r2;
< a href = "./assert-relation.html" class = "identifier" > BOOST_MPL_ASSERT_RELATION</ a > ( r1::value, ==, 84 );
< a href = "./assert-relation.html" class = "identifier" > BOOST_MPL_ASSERT_RELATION</ a > ( r2::value, ==, 84 );
</ pre >
</ div >
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< div class = "section" id = "id928" >
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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 = "./composition-and-argument-binding.html" > Composition and Argument Binding</ a > , < a class = "reference internal" href = "./invocation.html" > invocation</ a > , < a class = "reference internal" href = "./placeholders.html" > Placeholders</ a > , < a class = "reference internal" href = "./bind.html" > bind</ a > , < a class = "reference internal" href = "./quote.html" > quote</ a > , < a class = "reference internal" href = "./protect.html" > protect</ a > , < a class = "reference internal" href = "./apply.html" > apply</ a ></ p >
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<!-- Metafunctions/Composition and Argument Binding//bind |30 -->
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< table class = "footer" >< tr class = "footer" >< td class = "header-group navigation-bar" >< span class = "navigation-group" >< a href = "./placeholders.html" class = "navigation-link" > Prev</ a > < a href = "./bind.html" class = "navigation-link" > Next</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./placeholders.html" class = "navigation-link" > Back</ a > < a href = "./bind.html" class = "navigation-link" > Along</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./composition-and-argument-binding.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 >< 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
file LICENSE_1_0.txt or copy at < a class = "reference external" href = "http://www.boost.org/LICENSE_1_0.txt" target = "_top" > http://www.boost.org/LICENSE_1_0.txt</ a > )</ div ></ td ></ tr ></ table ></ body >
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