unique_ptr example for using void*

magic

#ifndef LIBFOO_H_INCLUDED
#define LIBFOO_H_INCLUDED

#pragma once

#include "libfoo_export.h"

#if defined(__cplusplus)
#define LIBFOO_NOEXCEPT noexcept
extern "C" {
#else
#define LIBFOO_NOEXCEPT
#endif

typedef struct foo_thing1 {
    int val;
} foo_thing1_t;

LIBFOO_API foo_thing1_t* foo_thing1_create() LIBFOO_NOEXCEPT;
LIBFOO_API void foo_thing1_destroy(foo_thing1_t* thing1) LIBFOO_NOEXCEPT;

typedef struct foo_thing2 {
    double val;
} foo_thing2_t;

LIBFOO_API foo_thing2_t* foo_thing2_create(double value1) LIBFOO_NOEXCEPT;
LIBFOO_API void foo_thing2_destroy(foo_thing2_t* thing2) LIBFOO_NOEXCEPT;

LIBFOO_API void foo_thing2_print(foo_thing2_t const* thing1) LIBFOO_NOEXCEPT;

#if defined(__cplusplus)
} // extern "C"
#endif

#endif // LIBFOO_H_INCLUDED

class FooThing2 {
private:
    static void dtor(void*);

public:

    using handle = std::unique_ptr<void, decltype(&FooThing2::dtor)>;

    FooThing2();

    void print();

private:
    handle _handle;
};

namespace {

    foo_thing2* cast(FooThing2::handle& h) {
        return reinterpret_cast<foo_thing2*>(h.get());
    }
}

FooThing2::FooThing2()
    : _handle(foo_thing2_create(1.0), &FooThing2::dtor) {
}

void FooThing2::print() {
    foo_thing2_print(cast(_handle));
}

void FooThing2::dtor(void* arg) {
    foo_thing2_destroy(static_cast<foo_thing2*>(arg));
}

int main(int argc, char* argv[]) {
#if 0
    libfoo::thing1_t thing1;
    libfoo::thing2_t thing2_a{0.0};
    libfoo::thing2_t thing2_b{42};

    thing2_b.value(thing1.value() * thing2_a.value());
    assert(thing2_b.value() == 0.0);

    foo_thing2_print(static_cast<foo_thing2_t*>(thing2_b));
    thing2_b.print();
#endif
    {
        FooThing2 magic;
        FooThing2 more_magic(std::move(magic));
        magic.print();
    }

    return EXIT_SUCCESS;
}