siyu798 <[email protected]> writes:
Hi Siyu,
> Your with-default fn is neat. So it appears there's no
> idiomatic/built-in clojure fn/macro to do parsing and wrapper
> functions such as follow would be needed to avoid typing the whole
> expression every time.
>
> (def parse-double (with-default #(Double. %) 0.0))
> (def parse-int (with-default #(Integer. %) 0))
You could pass the desired wrapper class as an argument to the function
and use reflection to create a new instance. I think all wrapper
classes have a constructor for parsing an String. Then you could write
(parse-wrapper Integer "111" 42) ==> 111
(parse-wrapper Double "111.1" 42.2) ==> 111.1
(parse-wrapper Byte "257" 42.2) ==> 42.3
Here's a (not really tested) version:
--8<---------------cut here---------------start------------->8---
(defn parse-wrapper [c v & [d]]
(try
(-> c (.getConstructor (into-array Class [String]))
(.newInstance (into-array Object [v])))
(catch Throwable _ d)))
--8<---------------cut here---------------end--------------->8---
Well, that doesn't save you much...
--8<---------------cut here---------------start------------->8---
(map #(parse-wrapper Double % 42.2)
["0" "1.5" "3.8e-1" "broken" "0x1.bP2" "Infinity" "NaN"])
==> (0.0 1.5 0.38 42.2 6.75 Infinity NaN)
--8<---------------cut here---------------end--------------->8---
And maybe it's a bit slower due to the use of reflection...
Bye,
Tassilo
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