Re: [PATCH] Let __attribute__((format(…))) accept OFStrings
js at webkeks.org
Tue Nov 26 10:31:19 PST 2013
Am 26.11.2013 um 19:23 schrieb Jean-Daniel Dupas <devlists at shadowlab.org>:
> That's a rather strange way to express it. UTF-16 is not more a workaround than UTF-32 or UTF-8. They are all first class encodings.
> Cocoa supports all Unicode planes and encode them using UTF-16 (or even ASCII internally) which is generally far more space efficient than using UTF-32.
> FWIW, it is even possible to use emoji in constant NSString generated at compilation time. So telling that Cocoa can only handle UCS-2 is plainly wrong.
How can a single unichar (which is typedef'd to unsigned short) store more than UCS-2? We are talking about the type for a single character (unichar vs. of_unichar_t) here. Strings internally use UTF-8 in ObjFW, but if you use characterAtIndex:, you get the whole character and not a surrogate. With Cocoa, you get a surrogate, as a single character can only be UCS-2. Try it yourself:
[@"😄" length] returns 2 in Cocoa. The same returns 1 in ObjFW, because it is one of_unichar_t.
[@"😄" characterAtIndex: 0] returns the surrogate in Cocoa. In ObjFW, it returns a single character 😄, because it fits into one of_unichar_t.
NSLog(@"%C", [@"😄" characterAtIndex: 0]);
It won't output 😄.
OTOH with ObjFW this:
of_log(@"%C", [@"😄" characterAtIndex: 0]);
will output 😄.
But in order to make this work, Clang may not assume that ObjFW is Cocoa and thus reject the format string.
And yet, the internal representation is not UTF-32 in ObjFW. So this has nothing to do with internal representation, but with how you export a single Unicode character - it's part of the API. And Cocoa decided to export a single Unicode characters as surrogates if necessary, because a unichar is an unsigned short and 😄 doesn't fit.
So where is it wrong what I said? It can handle UTF-16, sure. But it can't handle UCS-4 in a single character.
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