Re: ARC and reinterpret_cast
Re: ARC and reinterpret_cast
- Subject: Re: ARC and reinterpret_cast
- From: John McCall <email@hidden>
- Date: Mon, 09 Jul 2012 16:00:22 -0700
>>> From: Rick Mann <email@hidden>
>>> Subject: ARC and reinterpret_cast?
>>> Date: July 7, 2012 9:13:29 PM PDT
>>> To: Cocoa-Dev List <email@hidden>
>>>
>>> Hi. I'd like to write code like this:
>>>
>>> MyObject* foo = reinterpret_cast<__bridge MyObject*> (someVoidPointer);
>>>
>>> But the compiler doesn't like it. It's perfectly happy with:
>>>
>>> MyObject* foo = (__bridge MyObject) someVoidPointer;
>>>
>>> this is in a .mm file.
>>>
>>> The error is:
>>>
>>> error: type name requires a specifier or qualifier
>>> MyObject* me = reinterpret_cast<__bridge MyObject*> (inRefCon);
>>> ^
>>> error: expected '>'
>>> MyObject* me = reinterpret_cast<__bridge MyObject*> (inRefCon);
>>> ^
>>>>
>>> note: to match this '<'
>>> MyObject* me = reinterpret_cast<__bridge MyObject*> (inRefCon);
>>> ^
>>> Is it a bug in the compiler, or am I doing something wrong?
Well, it's definitely an ugly error message; that's worth a bug.
The answer is that reinterpret_cast is redundant with __bridge. Bridging
casts are essentially a different kind of named cast: they document intent
more precisely than the general cast syntax, and they impose their own
well-formedness rules about the operand and result type. So you're not
getting any extra safety here.
This is documented in the ARC specification:
http://clang.llvm.org/docs/AutomaticReferenceCounting.html#objects.operands.casts
3.2.4. Bridged casts
A bridged cast is a C-style cast annotated with . . .
In theory there's nothing preventing us from allowing these keywords on
named casts (although it would only be appropriate on reinterpret_cast),
but our sense is that doing so would only confuse the issue more by
suggesting subtle differences when none apply.
John.
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