Question

Given I have a type specifier as returned by method_copyReturnType(). In the GNU runtime delivered with the GCC there are various methods to work with such a type specifier like objc_sizeof_type(), objc_alignof_type() and others.

When using the Apple runtime there are no such methods.

How can I interpret a type specifier string (e.g. get the size of a type) using the Apple runtime without implementing an if/else or case switch for myself?

[update]

I am not able to use the Apple Foundation.

Answer 1

afaik, you’ll need to bake that info into your binary. just create a function which returns the sizeof and alignof in a struct, supports the types you must support, then call that function (or class method) for the info.

The program below shows you that many of the primitives are just one character. So the bulk of the function’s implementation could be a switch.

static void test(SEL sel) {
    Method method = class_getInstanceMethod([NSString class], sel);

    const char* const type = method_copyReturnType(method);

    printf("%s : %s\n", NSStringFromSelector(sel).UTF8String, type);

    free((void*)type);
}

int main(int argc, char *argv[]) {
    @autoreleasepool {

        test(@selector(init));
        test(@selector(superclass));
        test(@selector(isEqual:));
        test(@selector(length));

        return 0;
  }
}

and you could then use this as a starting point:

typedef struct t_pair_alignof_sizeof {
    size_t align;
    size_t size;
} t_pair_alignof_sizeof;

static t_pair_alignof_sizeof MakeAlignOfSizeOf(size_t align, size_t size) {
    t_pair_alignof_sizeof ret = {align, size};
    return ret;
}

static t_pair_alignof_sizeof test2(SEL sel) {
    Method method = class_getInstanceMethod([NSString class], sel);
    const char* const type = method_copyReturnType(method);
    const size_t length = strlen(type);

    if (1U == length) {
        switch (type[0]) {
            case '@' :
                return MakeAlignOfSizeOf(__alignof__(id), sizeof(id));
            case '#' :
                return MakeAlignOfSizeOf(__alignof__(Class), sizeof(Class));
            case 'c' :
                return MakeAlignOfSizeOf(__alignof__(signed char), sizeof(signed char));
            ...