[MacRuby-devel] Conforming to a protocol

[Charles Steinman]

In case anyone needs it in the meantime, here is a working
implementation of conformsToProtocol:

def conformsToProtocol(protocol)
   supported = %w( AProtocol SomeOtherProtocol YetAnotherProtocol
).map {|name| Protocol.protocolWithName name} # List the protocols you
want to conform to between the parns
   supported.any? {|candidate| protocol.isEqual candidate } or super
end

The reason this works is because Protocol *is* a real class, but it's
derived from a base class different from NSObject. Obviously we'll
want a better solution for MacRuby, but this will work in the
meantime.

— Chuck

On Wed, Nov 17, 2010 at 4:42 AM, Eloy Duran <eloy.de.enige at gmail.com> wrote:
> 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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