On Mon, Aug 20, 2012 at 10:06 AM, David Chisnall <[email protected]> wrote:
> It sounds like you're spending a lot of effort working around obscure
> corner cases that almost certainly will never appear in the wild.
>
It wasn't a lot of time, actually, at least until this problem cropped up
:-)
> CGPoint and NSPoint are supposed to be identical and code is allowed to
> cast between them and, more importantly, lots of existing code casts
> between arrays of NSPoint and arrays of CGPoint.
>
That's great, but despite it being the same, I still haven't seen this
guarantee in the docs. In fact, existence of NSPointFromCGPoint() and
NSPointToCGPoint() means it shouldn't be relied upon.
I do concur that because casting between these types is widespread, this
isn't much of a big deal. But, should we in the future go down the path of
treating separate structs as the same type just because they have the same
in-memory layout? Why would @encode even include the type name, then? Why
would NSValue provide access to objCType? Am I forbidden from comparing
these and making an informed decision on how to treat a data type based on
that? What if NSSize was supposed to be animated or treated differently
from NSPoint - should I lose the information that something was a NSSize
just because it has the same in-memory layout?
I'd love to work around this, but since I'm dealing with KVC and KVO, I
can't easily skip using NSValues to store structs and implement something
of my own.
Plus, it worked correctly, and now it's broken. :-)
> C structs are just blobs of memory. If they are structurally equivalent
> then, for all practical purposes, they are interchangeable.
In any case, there's still a bug, even if the original issue is about to be
dismissed. (I still consider that if I put one thing into the NSValue, I
should be getting the same thing out - even if the memory layout is the
same. Otherwise, let's also patch @encode in clang and gcc.)
If 'from' contains a NSValue with a 'NSPoint' in it (or something that
claims to be an NSPoint created through
from = [NSValue valueWithBytes: &fromPt objCType: @encode(CGPoint)];
the following still doesn't work and sets only the .x member:
CGPoint fromPt = { 0 }; [from getValue:&fromPt];
I'm sure it's a problem with getValue: since removing initialization of
fromPt means I end up with junk in .y.
So, the problems: I have a NSValue with a CGPoint in there, I can't tell
it's a CGPoint, and fetching it results in a failure. :-)
--
Ivan Vučica - [email protected]
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