callable.cpp
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// Boost.Convert test and usage example
// Copyright (c) 2009-2020 Vladimir Batov.
// Use, modification and distribution are subject to the Boost Software License,
// Version 1.0. See http://www.boost.org/LICENSE_1_0.txt.
#include "./test.hpp"
#if !defined(BOOST_CONVERT_CXX14)
int main(int, char const* []) { return 0; }
#else
#include <boost/convert.hpp>
#include <boost/convert/lexical_cast.hpp>
#include <functional>
using std::string;
using boost::convert;
using boost::lexical_cast;
//[callable_example1
void plain_old_func(string const& value_in, boost::optional<int>& value_out)
//]
{
try
{
value_out = lexical_cast<int>(value_in);
}
catch (...)
{
}
}
template<typename TypeIn, typename TypeOut>
void
convert_all(TypeIn const&, boost::optional<TypeOut>&)
{
}
template<typename Type>
void
assign(boost::optional<Type>& value_out, Type const& value_in)
{
value_out = value_in;
}
struct converter1
{
template<typename TypeIn, typename TypeOut>
void
operator()(TypeIn const&, boost::optional<TypeOut>&) const
{
}
};
//[callable_example4
struct take_double { void operator()(double, boost::optional<string>&) const {}};
struct take_int { void operator()(int, boost::optional<string>&) const {}};
//]
//[callable_example6
struct double_only
{
// Declared for all types.
template<typename TypeIn> void operator()(TypeIn, boost::optional<string>&) const;
};
// Defined only for certain types.
template<> void double_only::operator()<double>(double, boost::optional<string>&) const {}
//]
int
main(int, char const* [])
{
using func_type = std::function<void (string const& value_in, boost::optional<int>&)>;
char const* const str = "-12";
// Testing old-function-based converter.
//[callable_example2
int v01 = convert<int>(str, plain_old_func).value_or(-1);
//]
// Testing std::function-based converter.
int v02 = convert<int>(str, func_type(plain_old_func)).value_or(-1);
// Testing crazy std::bind-based converter.
//[callable_example3
int v03 = convert<int>(str,
std::bind(assign<int>, std::placeholders::_2,
std::bind(boost::lexical_cast<int, string>, std::placeholders::_1))).value_or(-1);
//]
BOOST_TEST(v01 == -12);
BOOST_TEST(v02 == -12);
BOOST_TEST(v03 == -12);
convert<int>(str, convert_all<string, int>);
convert<string>(11, convert_all<int, string>);
convert< int>(str, converter1());
convert<string>(11, converter1());
convert<string>(11.23, take_double());
convert<string>(11, take_int());
//[callable_example5
convert<string>(11, take_double()); // Compiler applies int-to-double promotion to call the converter.
convert<string>(11.23, take_int()); // Compiler applies double-to-int implicit truncation.
//]
//[callable_example7
convert<string>(11.23, double_only()); // Fine.
// convert<string>(11, double_only()); // Fails: undefined reference to double_only::operator()<int>
//]
return boost::report_errors();
}
#endif