Re: [Pyobjc-dev] "out" parameters and return values

[Mani G. <ma...@tu...>]

Ok, I'll put together some simplified code and post my results as soon
as I can (might be a couple days). In the meantime, here is the
protocol in question: ISyncSessionDriverDataSource
(http://developer.apple.com/documentation/Cocoa/Reference/ISyncSessionDriverDataSource_Protocol/Reference/Reference.html#//apple_ref/occ/intf/ISyncSessionDriverDataSource)

Kind regards,
Mani

On Thu, Feb 19, 2009 at 2:11 AM, Ronald Oussoren <ron...@ma...> wrote:
>
> On 19 Feb, 2009, at 5:16, Mani Ghasemlou wrote:
>
>> Thanks so much. Then, there must be something wrong with my code,
>> because I keep getting a crash when hitting this code. This however
>> rules out that my overall approach is wrong.
>
> Can you reproduce your crash in a smaller program? That would allow us to
> look at the code and could help pintpoint the issue (either something in
> your code or a bug in PyObjC).
>
> Is the method your writing overriding an existing method, or implementing an
> informal protocol?  PyObjC cannot deduce the right signature for methods
> with output arguments without that information. An easy way to check if
> that's your problem is to add some  decoration[1] to your code that
> explicitly sets the signature:
>
>   def returnIntWithError_(self, outError):
>        pass # body goes here
>   returnIntWithError_ = objc.selector(returnIntWithError_,
> signature='@@:o^@')
>
> Ronald
>
> [1] the reason for this strange formulation is that I wanted to write "a
> decorator", but noticed that the required decorator isn't actually part of
> PyObjC yet.
>
>>
>>
>> Kind regards,
>> Mani
>>
>> On Wed, Feb 18, 2009 at 4:17 PM, Ronald Oussoren <ron...@ma...>
>> wrote:
>>>
>>> Hi,
>>>
>>> You're approach is correct.
>>>
>>>>> def returnIntWithError_(self, outError):
>>>>> myError = NSError.errorWithDomain_code_userInfo_('myDomain', '1',
>>>>> objc.nil)
>>>>> myReturnVal = 1
>>>>> return myReturnVal, myError
>>>>
>>>
>>> As an optimization you could check if "outError is objc.NULL", if it is
>>> the
>>> caller isn't interested in the error value and you could return
>>> (myReturnVal, objc.NULL) instead of (myReturnVal, myError).   That's not
>>> really an issue here, but could help when it is hard to calculate the
>>> value
>>> of the output argument.
>>>
>>> BTW. Use "None" instead of "objc.nil", both have the same value and
>>> "objc.nil" is basicly only present to make it easier to translate ObjC
>>> code
>>> into Python. The same is true for objc.YES and objc.NO, those are aliases
>>> for True and False.
>>>
>>> Ronald
>>>
>>>
>>> On 17 Feb, 2009, at 20:51, Mani Ghasemlou wrote:
>>>
>>>> Just wanted to raise this question again, as I still haven't found a
>>>> solution.
>>>>
>>>> I've posted the same question on Cocoa-dev, also with no response:
>>>> http://www.cocoabuilder.com/archive/message/cocoa/2009/2/2/229316
>>>>
>>>> Would greatly appreciate any insights!
>>>>
>>>> Kind regards,
>>>> Mani
>>>>
>>>> On Mon, Feb 2, 2009 at 9:34 AM, Mani Ghasemlou <ma...@tu...> wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> From what I understand of the PyObjc documentation, "out" pointer
>>>>> variables (such as "NSError **outError") are actually appended to the
>>>>> list of return values for a bridge function.
>>>>>
>>>>> For example:
>>>>>
>>>>> int returnIntWithError: NSError **outError
>>>>>
>>>>> from Python would be invoked as:
>>>>>
>>>>> returned_int, returned_error = returnIntWithError_(None)
>>>>>
>>>>> I hope that my understanding of the above is correct.
>>>>>
>>>>> Now, my real question is to extend the above concept to the Python
>>>>> side, when we want to implement an informal protocol.  Let's say the
>>>>> protocol says that I have to implement the returnIntWithError:
>>>>> function as described above. How do I implement this function? Is the
>>>>> code below enough?
>>>>>
>>>>> def returnIntWithError_(self, outError):
>>>>> myError = NSError.errorWithDomain_code_userInfo_('myDomain', '1',
>>>>> objc.nil)
>>>>> myReturnVal = 1
>>>>> return myReturnVal, myError
>>>>>
>>>>> Note that I am completely ignoring the "outError" parameter. Does this
>>>>> look kosher?
>>>>>
>>>>> Thanks in advance for any help!
>>>>>
>>>>> Cheers,
>>>>> Mani
>>>>>
>>>>
>>>>
>>>>
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>
>