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106 lines
2.8 KiB
C++
106 lines
2.8 KiB
C++
// Boost.TypeErasure library
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//
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// Copyright 2011 Steven Watanabe
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//
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// Distributed under the Boost Software License Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// $Id$
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//[multifunction
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/*`
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(For the source of this example see
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[@boost:/libs/type_erasure/example/multifunction.cpp multifunction.cpp])
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This example implements an extension of Boost.Function that supports
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multiple signatures.
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[note This example uses C++11 features. You'll need a
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recent compiler for it to work.]
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*/
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#include <boost/type_erasure/any.hpp>
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#include <boost/type_erasure/builtin.hpp>
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#include <boost/type_erasure/callable.hpp>
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#include <boost/mpl/vector.hpp>
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#include <boost/variant.hpp>
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#include <boost/phoenix/core.hpp>
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#include <boost/phoenix/operator.hpp>
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#include <boost/range/algorithm.hpp>
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#include <algorithm>
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#include <vector>
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#include <string>
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#include <iostream>
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namespace mpl = boost::mpl;
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using namespace boost::type_erasure;
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namespace phoenix = boost::phoenix;
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// First of all we'll declare the multifunction template.
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// multifunction is like Boost.Function but instead of
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// taking one signature, it takes any number of them.
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template<class... Sig>
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using multifunction =
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any<
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mpl::vector<
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copy_constructible<>,
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typeid_<>,
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relaxed,
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callable<Sig>...
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>
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>;
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// Let's use multifunction to process a variant. We'll start
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// by defining a simple recursive variant to use.
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typedef boost::make_recursive_variant<
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int,
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double,
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std::string,
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std::vector<boost::recursive_variant_> >::type variant_type;
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typedef std::vector<variant_type> vector_type;
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// Now we'll define a multifunction that can operate
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// on the leaf nodes of the variant.
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typedef multifunction<void(int), void(double), void(std::string)> function_type;
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class variant_handler
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{
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public:
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void handle(const variant_type& arg)
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{
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boost::apply_visitor(impl, arg);
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}
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void set_handler(function_type f)
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{
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impl.f = f;
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}
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private:
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// A class that works with boost::apply_visitor
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struct dispatcher : boost::static_visitor<void>
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{
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// used for the leaves
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template<class T>
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void operator()(const T& t) { f(t); }
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// For a vector, we recursively operate on the elements
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void operator()(const vector_type& v)
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{
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boost::for_each(v, boost::apply_visitor(*this));
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}
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function_type f;
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};
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dispatcher impl;
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};
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int main() {
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variant_handler x;
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x.set_handler(std::cout << phoenix::val("Value: ") << phoenix::placeholders::_1 << std::endl);
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x.handle(1);
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x.handle(2.718);
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x.handle("The quick brown fox jumps over the lazy dog.");
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x.handle(vector_type{ 1.618, "Gallia est omnis divisa in partes tres", 42 });
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}
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//]
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