C++ shared libraries compatibility

README

In C shared libraries structs are usually allocate and returned by pointer 
incase any future items are add to a the struct. They usually look something
like this:

my_struct* init_my_struct();
void free_my_struct(my_struct*);

This gist is an attempt to mimic that with modern C++

LICENSE

Copyright (C) Freddy A Cubas "Superstar64"

Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.

main.cpp

#include <memory>
#include "shared.hpp"

int main() {
  auto safe = std::make_unique<Shared>();
}

makefile

CXXFLAGS =-fPIC -O3

main: main.o libshared.so
	$(CXX) main.o -Wl,-rpath=. -L. -lshared -o $@

%.asm: %.o
	objdump -drC $< > $@

main.o: shared.hpp
shared.o: shared.hpp

libshared.so: shared.o
	$(CXX) $^ -shared -o $@

shared.cpp

#define SHARED_CPP
#include "shared.hpp"

template std::unique_ptr<Shared> std::make_unique<Shared>();
template void std::default_delete<Shared>::operator()(Shared*) const;

shared.hpp

#pragma once
#include <memory>
#include <string>

struct Shared {
  int a;
  std::string b;

  friend std::unique_ptr<Shared> std::make_unique<Shared>();
  friend struct std::default_delete<Shared>;

 private:
  Shared() = default;
  ~Shared() = default;
};

// extern templates allow inlining, so we have to use a dirty hack
#ifndef SHARED_CPP
namespace std {
template <>
unique_ptr<Shared> make_unique<Shared>();
template <>
void default_delete<Shared>::operator()(Shared*) const;
}
#endif