On 14/06/2010 01:27, Paul Griffioen wrote:
> On Mon, 14 Jun 2010 00:41:51 +0200, Pascal Costanza wrote:
>
>> On 13/06/2010 20:24, Paul Griffioen wrote:
>>>
>>> Why do compilers warn about unused keyword in methods when (call-next-
>>> method) is used? For example when compiling
>>>
>>> (defclass some-class () ())
>>>
>>> (defmethod foo ((object some-class) some-arg&key some-key)
>>> (call-next-method))
>>>
>>> SBCL and LispWorks warn about keyword some-key (haven't tried other
>>> compilers). The keyword is passed to the next method so declaring it as
>>> unused seems wrong. And they don't warn about argument some-arg.
>>>
>>> Is there any reason for this? And is there a way to get rid of these
>>> warnings?
>>
>> If there is no need to use the keyword argument in the method body, it's
>> better to just omit it. You can just say this:
>>
>> (defmethod foo ((object some-class) some-arg&key)
>> ...)
>>
>> This doesn't work if the defgeneric form also mentions the particular
>> keyword argument in question, but maybe it shouldn't either, since it
>> doesn't seem to be necessary for all methods.
>>
>> The exact rules when you have to mention a keyword argument and when not
>> are in the HyperSpec in Section 7.6.5. Note that keyword arguments
>> require extra processing, so not mentioning them may be preferable. If
>> all else fails, (declare (ignore some-key)) always does the trick.
>>
>>
>> Pascal
>
> Thanks for the explanation and the reference. I didn't know these rules.
>
> In my case the keyword is mentioned in the generic function so I have to
> mention it in the method. I'm not sure if I want to remove the keywords
> in the generic function. Why do you say that the keyword doesn't seem
> necessary? I want the method to accept it but the default handling is
> sufficient.

In that case it's ok to have it in the defgeneric form.

> I was uncertain about an ignore declaration (or the ignorable that
> Raffael Cavallaro mentions) because the regular argument doesn't need it.
> Is such a declaration always valid? Because the keyword is used, although
> not visible. The declaration seems a bit strange when I read the code,
> but maybe I just have to get used to it.

You just have to get used to it.

'ignore is good when you know you don't want to use the variable. If you
then happen to use it anyway, you will get a warning, which may be helpful.

'ignorable is good when you don't care. I think this case occurs rarer
than 'ignore in manually written code, but can be very useful in macros
that generate function or method definitions.


Pascal

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