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< title > Chapter  1.  Boost.Functional/OverloadedFunction 1.0.0</ title >
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< a name = "boost_functional_overloadedfunction" ></ a > Chapter  1.  Boost.Functional/OverloadedFunction 1.0.0</ h2 ></ div >
< div >< div class = "author" >< h3 class = "author" >
< span class = "firstname" > Lorenzo</ span > < span class = "surname" > Caminiti < code class = "email" > < < a class = "email" href = "mailto:lorcaminiti@gmail.com" > lorcaminiti@gmail.com</ a > > </ code ></ span >
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< div >< p class = "copyright" > Copyright © 2011, 2012 Lorenzo Caminiti</ p ></ div >
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< a name = "boost_functional_overloadedfunction.legal" ></ a >< 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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< p >< b > Table of Contents</ b ></ p >
< dl >
< dt >< span class = "section" >< a href = "index.html#boost_functional_overloadedfunction.introduction" > Introduction</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/getting_started.html" > Getting
Started</ a ></ span ></ dt >
< dd >< dl >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.compilers_and_platforms" > Compilers
and Platforms</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.installation" > Installation</ a ></ span ></ dt >
</ dl ></ dd >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/tutorial.html" > Tutorial</ a ></ span ></ dt >
< dd >< dl >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.overloading" > Overloading</ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.without_function_types" > Without
Function Types</ a ></ span ></ dt >
</ dl ></ dd >
< dt >< span class = "section" >< a href = "reference.html" > Reference</ a ></ span ></ dt >
< dd >< dl >
< dt >< span class = "section" >< a href = "reference.html#header.boost.functional.overloaded_function_hpp" > Header < boost/functional/overloaded_function.hpp> </ a ></ span ></ dt >
< dt >< span class = "section" >< a href = "reference.html#header.boost.functional.overloaded_function.config_hpp" > Header < boost/functional/overloaded_function/config.hpp> </ a ></ span ></ dt >
</ dl ></ dd >
< dt >< span class = "section" >< a href = "boost_functional_overloadedfunction/acknowledgments.html" > Acknowledgments</ a ></ span ></ dt >
</ dl >
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< p >
This library allows to overload different functions into a single function object.
</ p >
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< div class = "section" >
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< div class = "titlepage" >< div >< div >< h2 class = "title" style = "clear: both" >
< a name = "boost_functional_overloadedfunction.introduction" ></ a >< a class = "link" href = "index.html#boost_functional_overloadedfunction.introduction" title = "Introduction" > Introduction</ a >
</ h2 ></ div ></ div ></ div >
< p >
Consider the following functions which have distinct signatures:
</ p >
< p >
</ p >
< pre class = "programlisting" >< span class = "keyword" > const</ span > < span class = "identifier" > std</ span >< span class = "special" > ::</ span >< span class = "identifier" > string</ span >< span class = "special" > & </ span > < span class = "identifier" > identity_s</ span >< span class = "special" > (</ span >< span class = "keyword" > const</ span > < span class = "identifier" > std</ span >< span class = "special" > ::</ span >< span class = "identifier" > string</ span >< span class = "special" > & </ span > < span class = "identifier" > x</ span >< span class = "special" > )</ span > < span class = "comment" > // Function (as pointer).</ span >
< span class = "special" > {</ span > < span class = "keyword" > return</ span > < span class = "identifier" > x</ span >< span class = "special" > ;</ span > < span class = "special" > }</ span >
< span class = "keyword" > int</ span > < span class = "identifier" > identity_i_impl</ span >< span class = "special" > (</ span >< span class = "keyword" > int</ span > < span class = "identifier" > x</ span >< span class = "special" > )</ span > < span class = "special" > {</ span > < span class = "keyword" > return</ span > < span class = "identifier" > x</ span >< span class = "special" > ;</ span > < span class = "special" > }</ span >
< span class = "keyword" > int</ span > < span class = "special" > (& </ span >< span class = "identifier" > identity_i</ span >< span class = "special" > )(</ span >< span class = "keyword" > int</ span >< span class = "special" > )</ span > < span class = "special" > =</ span > < span class = "identifier" > identity_i_impl</ span >< span class = "special" > ;</ span > < span class = "comment" > // Function reference.</ span >
< span class = "keyword" > double</ span > < span class = "identifier" > identity_d_impl</ span >< span class = "special" > (</ span >< span class = "keyword" > double</ span > < span class = "identifier" > x</ span >< span class = "special" > )</ span > < span class = "special" > {</ span > < span class = "keyword" > return</ span > < span class = "identifier" > x</ span >< span class = "special" > ;</ span > < span class = "special" > }</ span >
< span class = "identifier" > boost</ span >< span class = "special" > ::</ span >< span class = "identifier" > function</ span >< span class = "special" > < </ span >< span class = "keyword" > double</ span > < span class = "special" > (</ span >< span class = "keyword" > double</ span >< span class = "special" > )> </ span > < span class = "identifier" > identity_d</ span > < span class = "special" > =</ span > < span class = "identifier" > identity_d_impl</ span >< span class = "special" > ;</ span > < span class = "comment" > // Functor.</ span >
</ pre >
< p >
</ p >
< p >
Instead of calling them using their separate names (here < code class = "computeroutput" >< span class = "identifier" > BOOST_TEST</ span ></ code >
is equivalent to < code class = "computeroutput" >< span class = "identifier" > assert</ span ></ code > ):
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< a href = "#ftn.boost_functional_overloadedfunction.introduction.f0" class = "footnote" >< sup class = "footnote" >< a name = "boost_functional_overloadedfunction.introduction.f0" ></ a > [1]</ sup ></ a >
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</ p >
< p >
</ p >
< pre class = "programlisting" >< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity_s</ span >< span class = "special" > (</ span >< span class = "string" > "abc"</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "string" > "abc"</ span >< span class = "special" > );</ span >
< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity_i</ span >< span class = "special" > (</ span >< span class = "number" > 123</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "number" > 123</ span >< span class = "special" > );</ span >
< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity_d</ span >< span class = "special" > (</ span >< span class = "number" > 1.23</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "number" > 1.23</ span >< span class = "special" > );</ span >
</ pre >
< p >
</ p >
< p >
It is possible to use this library to create a single < a href = "http://en.wikipedia.org/wiki/Function_overloading" target = "_top" > overloaded</ a >
function object (or < a href = "http://en.wikipedia.org/wiki/Functor" target = "_top" > functor</ a > )
named < code class = "computeroutput" >< span class = "identifier" > identity</ span ></ code > that aggregates
together the calls to the specific functions (see also < a href = "../../test/functor.cpp" target = "_top" >< code class = "literal" > functor.cpp</ code ></ a >
and < a href = "../../test/identity.hpp" target = "_top" >< code class = "literal" > identity.hpp</ code ></ a > ):
</ p >
< p >
</ p >
< pre class = "programlisting" >< span class = "identifier" > boost</ span >< span class = "special" > ::</ span >< span class = "identifier" > overloaded_function</ span >< span class = "special" > < </ span >
< span class = "keyword" > const</ span > < span class = "identifier" > std</ span >< span class = "special" > ::</ span >< span class = "identifier" > string</ span >< span class = "special" > & </ span > < span class = "special" > (</ span >< span class = "keyword" > const</ span > < span class = "identifier" > std</ span >< span class = "special" > ::</ span >< span class = "identifier" > string</ span >< span class = "special" > & )</ span >
< span class = "special" > ,</ span > < span class = "keyword" > int</ span > < span class = "special" > (</ span >< span class = "keyword" > int</ span >< span class = "special" > )</ span >
< span class = "special" > ,</ span > < span class = "keyword" > double</ span > < span class = "special" > (</ span >< span class = "keyword" > double</ span >< span class = "special" > )</ span >
< span class = "special" > > </ span > < span class = "identifier" > identity</ span >< span class = "special" > (</ span >< span class = "identifier" > identity_s</ span >< span class = "special" > ,</ span > < span class = "identifier" > identity_i</ span >< span class = "special" > ,</ span > < span class = "identifier" > identity_d</ span >< span class = "special" > );</ span >
< span class = "comment" > // All calls via single `identity` function.</ span >
< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity</ span >< span class = "special" > (</ span >< span class = "string" > "abc"</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "string" > "abc"</ span >< span class = "special" > );</ span >
< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity</ span >< span class = "special" > (</ span >< span class = "number" > 123</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "number" > 123</ span >< span class = "special" > );</ span >
< span class = "identifier" > BOOST_TEST</ span >< span class = "special" > (</ span >< span class = "identifier" > identity</ span >< span class = "special" > (</ span >< span class = "number" > 1.23</ span >< span class = "special" > )</ span > < span class = "special" > ==</ span > < span class = "number" > 1.23</ span >< span class = "special" > );</ span >
</ pre >
< p >
</ p >
< p >
Note how the functions are called via a single overloaded function object
< code class = "computeroutput" >< span class = "identifier" > identity</ span ></ code > instead of using their
different names < code class = "computeroutput" >< span class = "identifier" > identity_s</ span ></ code > ,
< code class = "computeroutput" >< span class = "identifier" > identity_i</ span ></ code > , and < code class = "computeroutput" >< span class = "identifier" > identity_d</ span ></ code > .
</ p >
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< div class = "footnotes" >
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< br >< hr style = "width:100; align:left;" >
< div id = "ftn.boost_functional_overloadedfunction.introduction.f0" class = "footnote" >< p >< a href = "#boost_functional_overloadedfunction.introduction.f0" class = "para" >< sup class = "para" > [1] </ sup ></ a >
In most of the examples presented in this documentation, the Boost.Core/LightweightTest
(< code class = "literal" > boost/core/lightweight_test.hpp</ code > ) macro < code class = "computeroutput" >< span class = "identifier" > BOOST_TEST</ span ></ code > is used to check correctness
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conditions (conceptually similar to < code class = "computeroutput" >< span class = "identifier" > assert</ span ></ code > ).
A failure of the checked condition does not abort the execution of the program,
it will instead make < code class = "computeroutput" >< span class = "identifier" > boost</ span >< span class = "special" > ::</ span >< span class = "identifier" > report_errors</ span ></ code >
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return a non-zero program exit code. Using Boost.Core/LightweightTest allows
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to add the examples to the library regression tests so to make sure that
they always compile and run correctly.
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< td align = "left" >< p >< small > Last revised: January 10, 2018 at 15:18:50 GMT</ small ></ p ></ td >
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