Just copy/paste from my Counterclockwise REPL. :-)
- Chas
On Mar 30, 2013, at 11:54 PM, JvJ wrote:
> 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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