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< a name = "fusion.container.generation.functions.tiers" ></ a >< a href = "tiers.html" title = "Tiers" > Tiers</ a ></ h5 ></ div ></ div ></ div >
< p >
Tiers are sequences, where all elements are non-const reference types.
They are constructed with a call to a couple of < span class = "emphasis" >< em > tie</ em ></ span >
function templates. The succeeding sections document the various < span class = "emphasis" >< em > tier</ em ></ span >
flavors.
</ p >
< div class = "itemizedlist" >< ul type = "disc" >
< li >< a href = "list_tie.html" title = "list_tie" >< tt class = "computeroutput" >< span class = "identifier" > list_tie</ span ></ tt ></ a ></ li >
< li >< a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > vector_tie</ span ></ tt ></ a ></ li >
< li >< a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > map_tie</ span ></ tt ></ a ></ li >
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< p >
Example:
</ p >
< pre class = "programlisting" >
< span class = "keyword" > int</ span > < span class = "identifier" > i</ span >< span class = "special" > ;</ span > < span class = "keyword" > char</ span > < span class = "identifier" > c</ span >< span class = "special" > ;</ span > < span class = "keyword" > double</ span > < span class = "identifier" > d</ span >< span class = "special" > ;</ span >
< span class = "special" > ...</ span >
< a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > vector_tie</ span ></ tt ></ a >< span class = "special" > (</ span >< span class = "identifier" > i</ span >< span class = "special" > ,</ span > < span class = "identifier" > c</ span >< span class = "special" > ,</ span > < span class = "identifier" > a</ span >< span class = "special" > );</ span >
</ pre >
< p >
The < a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > vector_tie</ span ></ tt ></ a > function creates
a < a href = "../../vector.html" title = "vector" >< tt class = "computeroutput" >< span class = "identifier" > vector</ span ></ tt ></ a >
of type < tt class = "computeroutput" >< a href = "../../vector.html" title = "vector" >< tt class = "computeroutput" >< span class = "identifier" > vector</ span ></ tt ></ a >< span class = "special" > < </ span >< span class = "keyword" > int</ span >< span class = "special" > & ,</ span > < span class = "keyword" > char</ span >< span class = "special" > & ,</ span > < span class = "keyword" > double</ span >< span class = "special" > &> </ span ></ tt > . The same result could be achieved
with the call < a href = "make_vector.html" title = "make_vector" >< tt class = "computeroutput" >< span class = "identifier" > make_vector</ span ></ tt ></ a > (< a href = "http://www.boost.org/doc/html/ref.html" target = "_top" >< tt class = "computeroutput" >< span class = "identifier" > ref</ span ></ tt ></ a > (i), < a href = "http://www.boost.org/doc/html/ref.html" target = "_top" >< tt class = "computeroutput" >< span class = "identifier" > ref</ span ></ tt ></ a > (c), < a href = "http://www.boost.org/doc/html/ref.html" target = "_top" >< tt class = "computeroutput" >< span class = "identifier" > ref</ span ></ tt ></ a > (a))
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< sup > [< a name = "id544767" href = "#ftn.id544767" > 10</ a > ]</ sup >
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.
</ p >
< p >
A < span class = "emphasis" >< em > tie</ em ></ span > can be used to 'unpack' another tuple into
variables. E.g.:
</ p >
< pre class = "programlisting" >
< span class = "keyword" > int</ span > < span class = "identifier" > i</ span >< span class = "special" > ;</ span > < span class = "keyword" > char</ span > < span class = "identifier" > c</ span >< span class = "special" > ;</ span > < span class = "keyword" > double</ span > < span class = "identifier" > d</ span >< span class = "special" > ;</ span >
< a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > vector_tie</ span ></ tt ></ a >< span class = "special" > (</ span >< span class = "identifier" > i</ span >< span class = "special" > ,</ span > < span class = "identifier" > c</ span >< span class = "special" > ,</ span > < span class = "identifier" > d</ span >< span class = "special" > )</ span > < span class = "special" > =</ span > < a href = "make_vector.html" title = "make_vector" >< tt class = "computeroutput" >< span class = "identifier" > make_vector</ span ></ tt ></ a >< span class = "special" > (</ span >< span class = "number" > 1</ span >< span class = "special" > ,</ span >< span class = "char" > 'a'</ span >< span class = "special" > ,</ span > < span class = "number" > 5.5</ span >< span class = "special" > );</ span >
< span class = "identifier" > std</ span >< span class = "special" > ::</ span >< span class = "identifier" > cout</ span > < span class = "special" > << </ span > < span class = "identifier" > i</ span > < span class = "special" > << </ span > < span class = "string" > " "</ span > < span class = "special" > << </ span > < span class = "identifier" > c</ span > < span class = "special" > << </ span > < span class = "string" > " "</ span > < span class = "special" > << </ span > < span class = "identifier" > d</ span >< span class = "special" > ;</ span >
</ pre >
< p >
This code prints 1 a 5.5 to the standard output stream. A sequence unpacking
operation like this is found for example in ML and Python. It is convenient
when calling functions which return sequences.
</ p >
< a name = "fusion.container.generation.functions.tiers.ignore" ></ a >< h6 >
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< a name = "id545073" ></ a >
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< a href = "tiers.html#fusion.container.generation.functions.tiers.ignore" > Ignore</ a >
</ h6 >
< p >
There is also an object called < span class = "emphasis" >< em > ignore</ em ></ span > which allows
you to ignore an element assigned by a sequence. The idea is that a function
may return a sequence, only part of which you are interested in. For
example:
</ p >
< pre class = "programlisting" >
< span class = "keyword" > char</ span > < span class = "identifier" > c</ span >< span class = "special" > ;</ span >
< a href = "vector_tie.html" title = "vector_tie" >< tt class = "computeroutput" >< span class = "identifier" > vector_tie</ span ></ tt ></ a >< span class = "special" > (</ span >< span class = "identifier" > ignore</ span >< span class = "special" > ,</ span > < span class = "identifier" > c</ span >< span class = "special" > )</ span > < span class = "special" > =</ span > < a href = "make_vector.html" title = "make_vector" >< tt class = "computeroutput" >< span class = "identifier" > make_vector</ span ></ tt ></ a >< span class = "special" > (</ span >< span class = "number" > 1</ span >< span class = "special" > ,</ span > < span class = "char" > 'a'</ span >< span class = "special" > );</ span >
</ pre >
< div class = "footnotes" >
< br >< hr width = "100" align = "left" >
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< div class = "footnote" >< p >< sup > [< a name = "ftn.id544767" href = "#id544767" > 10</ a > ] </ sup >
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see < a href = "http://www.boost.org/doc/html/ref.html" target = "_top" > Boost.Ref</ a >
for details about < tt class = "computeroutput" >< span class = "identifier" > ref</ span ></ tt >
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< td align = "right" >< div class = "copyright-footer" > Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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Schwinger< p >
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at < a href = "http://www.boost.org/LICENSE_1_0.txt" target = "_top" > http://www.boost.org/LICENSE_1_0.txt</ a > )
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