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#include <iostream>
#include <functional>
 
struct protocol_callbacks
{
    using func_t = std::function<int(uint8_t*, size_t)>;
 
    protocol_callbacks(func_t a_reader, func_t a_writer) :
        reader(a_reader),
        writer(a_writer) {}
    func_t reader;
    func_t writer;
};
 
int writer(uint8_t*, size_t)
{
    std::cout << "function writer\n";
    return 0;
}
int reader(uint8_t*, size_t)
{
    std::cout << "function writer\n";
    return 0;
}
 
int bad_writer(uint16_t*, size_t) { return 0; }
 
int main ()
{
    int x = 9;
    protocol_callbacks pc1(reader, writer);
    protocol_callbacks pc2([=](uint8_t*, size_t)
                           {
                               std::cout << "lambda reader: " << x << "\n";
                               return 0;
                           },
                           [=](uint8_t*, size_t)
                           {
                               std::cout << "lambda writer: " << x << "\n";
                               return 0;
                           });
 
    pc1.reader(nullptr, 0);
    pc1.writer(nullptr, 0);
 
    pc2.reader(nullptr, 0);
    pc2.writer(nullptr, 0);
    protocol_callbacks pc3(bad_writer, reader);
}
 

In file included from prog.cpp:2:0:
/usr/include/c++/4.7/functional: In instantiation of ‘static _Res std::_Function_handler<_Res(_ArgTypes ...), _Functor>::_M_invoke(const std::_Any_data&, _ArgTypes ...) [with _Res = int; _Functor = int (*)(short unsigned int*, unsigned int); _ArgTypes = {unsigned char*, unsigned int}]’:
/usr/include/c++/4.7/functional:2298:6:   required from ‘std::function<_Res(_ArgTypes ...)>::function(_Functor, typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type) [with _Functor = int (*)(short unsigned int*, unsigned int); _Res = int; _ArgTypes = {unsigned char*, unsigned int}; typename std::enable_if<(! std::is_integral<_Functor>::value), std::function<_Res(_ArgTypes ...)>::_Useless>::type = std::function<int(unsigned char*, unsigned int)>::_Useless]’
prog.cpp:48:46:   required from here
/usr/include/c++/4.7/functional:1912:40: error: cannot convert ‘unsigned char*’ to ‘short unsigned int*’ in argument passing

Standard output is empty