Mark Engelberg <[email protected]> writes:
> filter works just as well with a function that returns true and false,
> so that's not a particularly good example.
Calling the set as if it is a fn is a short-hand for "get", that is
retrieving an element from the set. Why would you want to do this, when
to look it up you need to know what element is? Sets are based on
value-equality not reference-equality. Thus you can have an object in
the set that is equal to your lookup key but not identical. A simple
example is anything with metadata attached:
(def myset #{(with-meta 'foo {:something 1})})
Now I know what the symbol is but I want to retrieve the metadata from
the version that's in the set:
(meta (myset 'foo))
;;-> {:something 1}
Another use would interning -- returning a canonical version of an
object.
Cheers,
Alex
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