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< a name = "boost_functional_overloadedfunction" > < / a > Chapter  1.  Boost.Functional/OverloadedFunction 1.0.0< / h2 > < / div >
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< 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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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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< 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 >
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< 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 >
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< 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 >
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< dt > < span class = "section" > < a href = "boost_functional_overloadedfunction/acknowledgments.html" > Acknowledgments< / a > < / span > < / dt >
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< p >
This library allows to overload different functions into a single function object.
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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 >
< / div >
< 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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