Also, nice syntax highlighting! How'd you do that?
On Saturday, 30 March 2013 23:54:03 UTC-4, JvJ wrote:
>
> get-method. Thanks, that was exactly what I was looking for!
>
> On Saturday, 30 March 2013 07:20:54 UTC-4, Chas Emerick wrote:
>>
>> On Mar 30, 2013, at 12:00 AM, George Oliver wrote:
>>
>>
>>
>> On Friday, March 29, 2013 6:19:19 PM UTC-7, JvJ wrote:
>>>
>>> Is it possible to invoke a particular multimethod and bypass the
>>> dispatch function?
>>>
>>> For instance, suppose that I have a multimethod with a dispatch value of
>>> ::foo, and it's a really complex method.
>>>
>>> Now, I want all cases where the dispatch function returns nil to use the
>>> same multimethod. Is there a way I can intercept the nil and
>>> pass it directly on to the ::foo multimethod?
>>>
>>
>> You could use the default multimethod to catch nil, and then call the
>> multi with ::foo.
>>
>>
>> That will only work if the dispatch fn is identity or similar.
>>
>> If you control the dispatch fn, then you don't need to "intercept nil" --
>> just returning ::foo from the dispatch fn when it might otherwise return
>> nil will get you to the method you want.
>>
>> If you *don't* control the dispatch fn, but you're providing the methods
>> for :foo and nil, then you can use `get-method` to obtain the method
>> associated with a particular dispatch value:
>>
>> => (*defmulti* foo :bar)
>> #'user/foo
>> => (*defmethod* foo :baz
>> [x]
>> (str x))
>> #<MultiFn clojure.lang.MultiFn@6194a872>
>> => (*defmethod* foo :default
>> [x]
>> ((get-method foo :baz) x))
>> #<MultiFn clojure.lang.MultiFn@6194a872>
>> => (foo {:bar :baz})
>> "{:bar :baz}"
>> => (foo {:some :other :value :here})
>> "{:some :other, :value :here}"
>>
>> Of course, if the functionality you need is available as a separate
>> top-level fn, and you can avoid the extra effective dispatch through the
>> multimethod, all the better.
>>
>> Cheers,
>>
>> - Chas
>>
>>
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