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< title > The MPL Reference Manual: begin</ title >
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< body class = "docframe refmanual" >
< table class = "header" >< tr class = "header" >< td class = "header-group navigation-bar" >< span class = "navigation-group" >< a href = "./back.html" class = "navigation-link" > Prev</ a > < a href = "./clear.html" class = "navigation-link" > Next</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./back.html" class = "navigation-link" > Back</ a > < a href = "./clear.html" class = "navigation-link" > Along</ a ></ span >< span class = "navigation-group-separator" > | </ span >< span class = "navigation-group" >< a href = "./intrinsic-metafunctions.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 = "./sequences.html" class = "navigation-link" > Sequences</ a > / < a href = "./intrinsic-metafunctions.html" class = "navigation-link" > Intrinsic Metafunctions</ a > / < a href = "./begin.html" class = "navigation-link" > begin</ a ></ td >
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< div class = "section" id = "begin" >
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< h1 >< a class = "toc-backref" href = "./intrinsic-metafunctions.html#id1428" > begin</ a ></ h1 >
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< div class = "section" id = "id202" >
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< h3 >< a class = "subsection-title" href = "#synopsis" name = "synopsis" > Synopsis</ a ></ h3 >
< pre class = "literal-block" >
template<
typename X
>
struct < a href = "./begin.html" class = "identifier" > begin</ a >
{
typedef < em > unspecified</ em > type;
};
</ pre >
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< div class = "section" id = "id203" >
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< h3 >< a class = "subsection-title" href = "#description" name = "description" > Description</ a ></ h3 >
< p > Returns an iterator that points to the first element of the sequence. If
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the argument is not a < a class = "reference internal" href = "./forward-sequence.html" > Forward Sequence</ a > , returns < a class = "reference internal" href = "./void.html" > void_</ a > .</ p >
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</ div >
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< div class = "section" id = "id204" >
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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/begin_end.hpp" class = "header" > boost/mpl/begin_end.hpp</ a > >
</ pre >
</ div >
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< div class = "section" id = "id205" >
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< h3 >< a class = "subsection-title" href = "#model-of" name = "model-of" > Model of</ a ></ h3 >
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< p >< a class = "reference internal" href = "./tag-dispatched-metafunction.html" > Tag Dispatched Metafunction</ a ></ p >
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</ div >
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< div class = "section" id = "id206" >
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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 = "22%" />
< col width = "60%" />
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< 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 > A type whose begin iterator, if any, will be
returned.</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id207" >
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< h3 >< a class = "subsection-title" href = "#expression-semantics" name = "expression-semantics" > Expression semantics</ a ></ h3 >
< p > For any arbitrary type < tt class = "literal" >< span class = "pre" > x</ span ></ tt > :</ p >
< pre class = "literal-block" >
typedef < a href = "./begin.html" class = "identifier" > begin</ a > < x> ::type first;
</ 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" />
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< tr class = "field" >< th class = "field-name" > Return type:</ th >< td class = "field-body" >< a class = "reference internal" href = "./forward-iterator.html" > Forward Iterator</ a > or < a class = "reference internal" href = "./void.html" > void_</ a > .</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Semantics:</ th >< td class = "field-body" > If < tt class = "literal" >< span class = "pre" > x</ span ></ tt > is a < a class = "reference internal" href = "./forward-sequence.html" > Forward Sequence</ a > , < tt class = "literal" >< span class = "pre" > first</ span ></ tt > is an iterator pointing to the
first element of < tt class = "literal" >< span class = "pre" > s</ span ></ tt > ; otherwise < tt class = "literal" >< span class = "pre" > first</ span ></ tt > is < a class = "reference internal" href = "./void.html" > void_</ a > .</ td >
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</ tr >
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< tr class = "field" >< th class = "field-name" > Postcondition:</ th >< td class = "field-body" > If < tt class = "literal" >< span class = "pre" > first</ span ></ tt > is an iterator, it is either dereferenceable or past-the-end; it
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is past-the-end if and only if < tt class = "literal" >< span class = "pre" >< a href = "./size.html" class = "identifier" > size</ a > < x> ::value</ span > < span class = "pre" > ==</ span > < span class = "pre" > 0</ span ></ tt > .</ td >
</ tr >
</ tbody >
</ table >
</ div >
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< div class = "section" id = "id208" >
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< h3 >< a class = "subsection-title" href = "#complexity" name = "complexity" > Complexity</ a ></ h3 >
< p > Amortized constant time.</ p >
</ div >
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< div class = "section" id = "id209" >
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< h3 >< a class = "subsection-title" href = "#example" name = "example" > Example</ a ></ h3 >
< pre class = "literal-block" >
typedef < a href = "./vector.html" class = "identifier" > vector</ a > < unsigned char,unsigned short,
unsigned int,unsigned long > unsigned_types;
typedef < a href = "./begin.html" class = "identifier" > begin</ a > < unsigned_types> ::type iter;
< a href = "./assert.html" class = "identifier" > BOOST_MPL_ASSERT</ a > (( is_same< < a href = "./deref.html" class = "identifier" > deref</ a > < iter> ::type, unsigned char > ));
< a href = "./assert.html" class = "identifier" > BOOST_MPL_ASSERT</ a > (( is_same< < a href = "./begin.html" class = "identifier" > begin</ a > < int> ::type, < a href = "./void.html" class = "identifier" > void_</ a > > ));
</ pre >
</ div >
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< div class = "section" id = "id210" >
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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 = "./iterators.html" > Iterators</ a > , < a class = "reference internal" href = "./forward-sequence.html" > Forward Sequence</ a > , < a class = "reference internal" href = "./end.html" > end</ a > , < a class = "reference internal" href = "./size.html" > size</ a > , < a class = "reference internal" href = "./empty.html" > empty</ a ></ p >
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<!-- Sequences/Intrinsic Metafunctions//clear -->
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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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