source: libcfa/src/virtual_dtor.hfa

#pragma once

// inline virtual_dtor to have a virtual dtor.
// when using this, delete() is also virtual and will be called on the right address
// using free() directly on polymorphic types may result in unaligned memory deallocation
//     in multi-inheritance or in single inheritance if the inline isn't the first field

// This supports virtual dtors for both single and multiple inheritance,
// however it does not support multiple inheritance of the virtual_dtor. e.g.:
//     given struct A { inline virtual_dtor; } and struct B { inline virtual_dtor; }
//     struct C { inline A; inline B; } will result in undefined behaviour
struct virtual_dtor {
    void (*__virtual_dtor_ptr)(virtual_dtor &);
    void * __virtual_obj_start;
};

// the following routines are used by the compiler and should not be called directly
static inline void __CFA_set_virt_dtor( virtual_dtor & this, void (*v_dtor)(virtual_dtor &)) {
    this.__virtual_dtor_ptr = v_dtor;
}
static inline void __CFA_set_virt_start( virtual_dtor & this, void * start) {
    this.__virtual_obj_start = start;
}
static inline void __CFA_setup_dtor( virtual_dtor & this ) with(this) {
    __virtual_dtor_ptr = 0p;
    __virtual_obj_start = &this;
}
static inline bool __CFA_dtor_shutdown( virtual_dtor & this ) with(this) {
    if ( __virtual_dtor_ptr == 1p ) return true; // stop base dtors from being called twice
    if ( __virtual_dtor_ptr ) {
        void (*dtor_ptr)(virtual_dtor &) = __virtual_dtor_ptr;
        __virtual_dtor_ptr = 0p;
        dtor_ptr(*((virtual_dtor *)__virtual_obj_start)); // call most derived dtor
        __virtual_dtor_ptr = 1p; // stop base dtors from being called twice
        return true;
    }
    return false;
}
static inline void __CFA_virt_free( virtual_dtor & this ) { free( this.__virtual_obj_start ); }
static inline void * __CFA_get_virt_start( virtual_dtor & this ) { return this.__virtual_obj_start; }
static inline void ?{}( virtual_dtor & this ) {}
static inline void ^?{}( virtual_dtor & this ) {}