of course I missed something :-(
2011/1/25 Laurent PETIT <laurent.pe...@gmail.com>:
> 2011/1/25 Ken Wesson <kwess...@gmail.com>:
>> On Mon, Jan 24, 2011 at 7:32 PM, Laurent PETIT <laurent.pe...@gmail.com>
>> wrote:
>>> 2011/1/25 Ken Wesson <kwess...@gmail.com>:
>>>> Are we generally agreed that we want to preserve the body exception,
>>>> if any, else the close exception, if any, else the body return value?
>>>>
>>>> Then, without further ado:
>>>>
>>>> (defmacro with-open2 [binding-exprs & body]
>>>> (if (> (count binding-exprs) 2)
>>>> `(with-open2 ~(vec (take 2 binding-exprs))
>>>> (with-open2 ~(vec (drop 2 binding-exprs))
>>>> ~@body))
>>>> (let [[sym expr] binding-exprs]
>>>> `(let [~sym ~expr
>>>> res# (try
>>>> [(do ~@body)]
>>>> (catch Throwable t# t#))]
>>>> (if (vector? res#) ; body didn't throw
>>>> (do
>>>> (.close ~sym) ; so let close throw
>>>> (res# 0))
>>>> (do ; body threw
>>>> (try (.close ~sym) (catch Throwable _#)) ; eat close exception
>>>> (throw res#))))))) ; and rethrow body exception
>>>>
>>>> user=> (with-open [x (Foo.)] (doit x))
>>>> #<CompilerException java.lang.Exception: close exception
>>>> (NO_SOURCE_FILE:242)>
>>>> user=> (with-open2 [x (Foo.)] (doit x))
>>>> #<CompilerException java.lang.Exception: doit exception
>>>> (NO_SOURCE_FILE:40)>
>>>
>>> What about starting from the current definition of with-open in
>>> clojure.core, improving upon it (and at the same time, not building
>>> intermediate wrapper vector) :
>>>
>>> (in-ns 'clojure.core)
>>> (defmacro with-open
>>> "bindings => [name init ...]
>>>
>>> Evaluates body in a try expression with names bound to the values
>>> of the inits, and a finally clause that calls (.close name) on each
>>> name in reverse order."
>>> {:added "1.0"}
>>> [bindings & body]
>>> (assert-args with-open
>>> (vector? bindings) "a vector for its binding"
>>> (even? (count bindings)) "an even number of forms in binding vector")
>>> (cond
>>> (= (count bindings) 0) `(do ~@body)
>>> (symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
>>> (try
>>> (let [res# (with-open ~(subvec
>>> bindings 2) ~@body)]
>>> ;body didn't throw
>>> (. ~(bindings 0) close)
>>> res#)
>>> (catch Throwable t#
>>> (try (. ~(bindings 0) close) (catch
>>> Throwable _)) ; eat close exception
>>> (throw t#)))) ; and rethrow body exception
>>> :else (throw (IllegalArgumentException.
>>> "with-open only allows Symbols in bindings"))))
>>
>> Ah, I guess it may be a bit cleaner to just eschew "finally"
>> altogether and close in the try and in the catch. The one thing that's
>> a bit icky about that is that if the body close throws, the catch
>> clause tries to close the stream again. On the other hand, my
>> version's vector wrap is a bit icky, perhaps. :)
>>
>> Yours works if the binding vector is empty, too; I suppose that's a
>> good idea. You've also incorporated the core version's error reporting
>> code. If this makes it into core in any form it should probably
>> include those features. :)
>
> What about this version which gets rid of the double call to close ?
> Did I miss something (it's getting late here) ?
>
> (in-ns 'clojure.core)
> (defmacro with-open
> "bindings => [name init ...]
>
> Evaluates body in a try expression with names bound to the values
> of the inits, and a finally clause that calls (.close name) on each
> name in reverse order."
> {:added "1.0"}
> [bindings & body]
> (assert-args with-open
> (vector? bindings) "a vector for its binding"
> (even? (count bindings)) "an even number of forms in binding vector")
> (cond
> (= (count bindings) 0) `(do ~@body)
> (symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
> (try
> (with-open ~(subvec bindings 2) ~@body)
> (catch Throwable t#
> (try (. ~(bindings 0) close) (catch
> Throwable _)) ; eat close exception
> (throw t#))) ; and rethrow body exception
> (. ~(bindings 0) close))
> :else (throw (IllegalArgumentException.
> "with-open only allows Symbols in bindings"))))
>
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