[MacRuby-devel] Conforming to a protocol

[Eloy Duran]

Regardless of the current state, having a real Protocol class and objects that you can use to check against should be the goal. Let's discuss this further on the ticket from now on, for completeness sake.

On Nov 17, 2010, at 12:44 PM, Thibault Martin-Lagardette wrote:

> These structures are currently handled by Foundation's BridgeSupport file (/System/Library/Frameworks/Foundation.framework/Resources/BridgeSupport/Foundation.bridgesupport)
> 	<struct name='NSPoint' type64='{CGPoint=&quot;x&quot;d&quot;y&quot;d}' type='{_NSPoint=&quot;x&quot;f&quot;y&quot;f}'/>
> 	<struct name='NSRange' type64='{_NSRange=&quot;location&quot;Q&quot;length&quot;Q}' type='{_NSRange=&quot;location&quot;I&quot;length&quot;I}'/>
> It's not very humanly readable, but MacRuby understands what this means, and then knows NSPoint is a structure :-).
> 
> However, just for proving myself wrong, there IS a Protocol Obj-C objet ( see http://opensource.apple.com/source/objc4/objc4-437.1/runtime/Protocol.h ).
> But I think my point stands, as I do think what is returned is the C struct, not the class.
> I think Laurent might know a little better though :-)
> 
> -- 
> Thibault Martin-Lagardette
> 
> 
> 
> On Nov 17, 2010, at 12:19, Martijn Walraven wrote:
> 
>> Thanks for opening a ticket and describing the issue so well! 
>> 
>> I'm not sure how this should be solved, but I was wondering how things currently work for other C structs like NSRect or NSPoint. Are these handled as special cases, or is there a more general way to deal with C structs?
>> 
>> Would it make sense to think about somehow mapping C structs to the Ruby Struct class, or maybe a special CStruct class? It would be nice if this at least offered a way to perform equality checks (==, eql?, equals?). For structs that have defined attributes it would be great if this allowed getting and setting attribute values (similar to what you can do with NSRect and NSPoint).
>> 
>> I might be totally off, so maybe someone who knows more about the internals of MacRuby can comment?
>> 
>> On Nov 17, 2010, at 11:33 , Thibault Martin-Lagardette wrote:
>> 
>>> This is because protocols, in the Obj-C runtime, are not Obj-C objets per say, they are C structs.
>>> +protocolWithName returns an (id) (aka obj-c objet), but the actual returned pointer is just a pointer to a C struct, which causes the runtime to issue those warnings. It says "Hey, this method returned an objet, but it doesn't look like one!". Which is expected, but this should be improved.
>>> While it is true that in the Obj-C runtime, classes and objects are C structs too, they are obviously not the same kind of structures, which is why it doesn't work :-).
>>> 
>>> In MacRuby, `Protocol` IS a real Obj-C objet, but not what the +protocolWithName method returns. This means that whatever you do with the returned valiue, it will crash, because it is not a real objet, and thus does not respond to any message.
>>> This also means that you cannot even do something like that:
>>> 	Protocol.protocolWithName("NSCoding") == Protocol.protocolWithName("NSCoding")
>>> Simply because doing this will call the `#==` method on the left-most value, which is a C struct for a protocol, and not an Obj-C object.
>>> 
>>> I created https://www.macruby.org/trac/ticket/999 , related to protocols.
>>> Please be aware that the attached patch still does not make it possible to override conformsToProtocol:, because calling `#==` on non-objets will crash, which is why I think MacRuby could handle Protocols a little better, right now I'm not sure it's "usable" per say.
>>> 
>>> Sorry if I do repeat myself a little, but I want to make sure you understand why this does not work yet, and what you can and cannot do with protocols as of today :-).
>>> 
>>> -- 
>>> Thibault Martin-Lagardette
>> 
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