NSCopying+memcpy.m

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

@interface MyObject : NSObject <NSCopying> {
    @package NSUInteger _first;
    @package NSInteger _second;
    @package BOOL _third;
}
@end

@implementation MyObject

- (nonnull id)copyWithZone:(nullable NSZone *)zone { 
    id copy = [[self class] new];
    
    if (copy) {
        unsigned int ivarsCount;
        Ivar *ivars = class_copyIvarList([MyObject class], &ivarsCount);
        
        ptrdiff_t minOffset = ivar_getOffset(ivars[0]);
        ptrdiff_t maxOffset = ivar_getOffset(ivars[ivarsCount - 1]);
        
        // https://github.com/opensource-apple/objc4/blob/cd5e62a5597ea7a31dccef089317abb3a661c154/runtime/objc-runtime-new.h#L236
        uint32_t lastIvarSize = *(uint32_t *)((uintptr_t)ivars[ivarsCount - 1] + sizeof(int32_t *) + sizeof(const char *) + sizeof(const char *) + sizeof(uint32_t));
        
        free(ivars);
        
        const void *src = (const void *)((uintptr_t)self + minOffset);
        void *dst = (void *)((uintptr_t)copy + minOffset);
        
        memcpy(dst, src, maxOffset - minOffset + lastIvarSize);
    }
    
    return copy;
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MyObject *myObject_1 = [MyObject new];
        myObject_1->_first = 3;
        myObject_1->_second = 2;
        myObject_1->_third = YES;
        
        MyObject *myObject_2 = [myObject_1 copy];
        
        assert(myObject_1->_first == myObject_2->_first);
        assert(myObject_1->_second == myObject_2->_second);
        assert(myObject_1->_third == myObject_2->_third);
    }
    
    return 0;
}