#define DECL_CONST_CAST_OF(CCTYPE) \
    union { const CCTYPE *__c_ptr; CCTYPE *__ptr; } __ptr_u

#define const_cast(b) (__ptr_u.__c_ptr = (b), __ptr_u.__ptr)

DECL_CONST_CAST_OF(opcode_t);

self->data  = const_cast(cursor)