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#ifndef POLYMORPHISM_H
#define POLYMORPHISM_H
/* Macros to declare inheriting types, and to (down-)cast and up-cast. */
#define DERIVE_FROM_TYPE(t) t t##_parent
#define STATIC_CAST(to, obj) (&(obj)->to##_parent)
#ifdef __GNUC__
#define STATIC_UPCAST(to, from, obj) __extension__({ \
static_assert(__builtin_types_compatible_p(from, __typeof(*(obj))), \
"Invalid upcast object from type"); \
(to*)((char*)(obj) - offsetof(to, from##_parent)); \
})
#else
#define STATIC_UPCAST(to, from, obj) ((to*)((char*)(obj) - offsetof(to, from##_parent)))
#endif
/* Defines method forwards, which call the given parent's (T2's) implementation. */
#define DECLARE_FORWARD(T1, T2, rettype, func) \
rettype T1##_##func(T1 *obj) \
{ return T2##_##func(STATIC_CAST(T2, obj)); }
#define DECLARE_FORWARD1(T1, T2, rettype, func, argtype1) \
rettype T1##_##func(T1 *obj, argtype1 a) \
{ return T2##_##func(STATIC_CAST(T2, obj), a); }
#define DECLARE_FORWARD2(T1, T2, rettype, func, argtype1, argtype2) \
rettype T1##_##func(T1 *obj, argtype1 a, argtype2 b) \
{ return T2##_##func(STATIC_CAST(T2, obj), a, b); }
#define DECLARE_FORWARD3(T1, T2, rettype, func, argtype1, argtype2, argtype3) \
rettype T1##_##func(T1 *obj, argtype1 a, argtype2 b, argtype3 c) \
{ return T2##_##func(STATIC_CAST(T2, obj), a, b, c); }
/* Defines method thunks, functions that call to the child's method. */
#define DECLARE_THUNK(T1, T2, rettype, func) \
static rettype T1##_##T2##_##func(T2 *obj) \
{ return T1##_##func(STATIC_UPCAST(T1, T2, obj)); }
#define DECLARE_THUNK1(T1, T2, rettype, func, argtype1) \
static rettype T1##_##T2##_##func(T2 *obj, argtype1 a) \
{ return T1##_##func(STATIC_UPCAST(T1, T2, obj), a); }
#define DECLARE_THUNK2(T1, T2, rettype, func, argtype1, argtype2) \
static rettype T1##_##T2##_##func(T2 *obj, argtype1 a, argtype2 b) \
{ return T1##_##func(STATIC_UPCAST(T1, T2, obj), a, b); }
#define DECLARE_THUNK3(T1, T2, rettype, func, argtype1, argtype2, argtype3) \
static rettype T1##_##T2##_##func(T2 *obj, argtype1 a, argtype2 b, argtype3 c) \
{ return T1##_##func(STATIC_UPCAST(T1, T2, obj), a, b, c); }
#define DECLARE_THUNK4(T1, T2, rettype, func, argtype1, argtype2, argtype3, argtype4) \
static rettype T1##_##T2##_##func(T2 *obj, argtype1 a, argtype2 b, argtype3 c, argtype4 d) \
{ return T1##_##func(STATIC_UPCAST(T1, T2, obj), a, b, c, d); }
/* Defines the default functions used to (de)allocate a polymorphic object. */
#define DECLARE_DEFAULT_ALLOCATORS(T) \
static void* T##_New(size_t size) { return al_malloc(16, size); } \
static void T##_Delete(void *ptr) { al_free(ptr); }
/* Helper to extract an argument list for virtual method calls. */
#define EXTRACT_VCALL_ARGS(...) __VA_ARGS__))
/* Call a "virtual" method on an object, with arguments. */
#define V(obj, func) ((obj)->vtbl->func((obj), EXTRACT_VCALL_ARGS
/* Call a "virtual" method on an object, with no arguments. */
#define V0(obj, func) ((obj)->vtbl->func((obj) EXTRACT_VCALL_ARGS
/* Helper to extract an argument list for NEW_OBJ calls. */
#define EXTRACT_NEW_ARGS(...) __VA_ARGS__); \
} \
} while(0)
/* Allocate and construct an object, with arguments. */
#define NEW_OBJ(_res, T) do { \
_res = T##_New(sizeof(T)); \
if(_res) \
{ \
memset(_res, 0, sizeof(T)); \
T##_Construct(_res, EXTRACT_NEW_ARGS
/* Allocate and construct an object, with no arguments. */
#define NEW_OBJ0(_res, T) do { \
_res = T##_New(sizeof(T)); \
if(_res) \
{ \
memset(_res, 0, sizeof(T)); \
T##_Construct(_res EXTRACT_NEW_ARGS
/* Destructs and deallocate an object. */
#define DELETE_OBJ(obj) do { \
if((obj) != NULL) \
{ \
V0((obj),Destruct)(); \
V0((obj),Delete)(); \
} \
} while(0)
/* Helper to get a type's vtable thunk for a child type. */
#define GET_VTABLE2(T1, T2) (&(T1##_##T2##_vtable))
/* Helper to set an object's vtable thunk for a child type. Used when constructing an object. */
#define SET_VTABLE2(T1, T2, obj) (STATIC_CAST(T2, obj)->vtbl = GET_VTABLE2(T1, T2))
#endif /* POLYMORPHISM_H */
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