aaa ok this is clearer now...I guess I never wanted/tried to do that -
it seems plain weird to me since I know that there is a try/finally
hidden in there and escaping its scope will render the stream useless by
closing it. anyway thanks for the quick and clear response :)
If you 're dealing a lot with file io, i can understand why you might
think this is still boilerplate (albeit massively less than Java) but I
imagine wrapping with-open/doseq/line-seq in a macro that accepts some
forms to execute within it would be trivial...
Jim
On 07/11/12 19:09, Dave Ray wrote:
There aren't any problems with with-open/doseq/line-seq. The issue is
with with-open/line-seq. For example, it's instinctive (at least for
me anyway) to want to write a function like this:
(defn get-records [file-name]
(with-open [r (reader file-name)]
(line-seq r)))
Of course, the problem here is that the lazy sequence "escapes" the
with-open scope and you get an exception when you start consuming it.
And given a sequence there's no mechanism to say "I'm done with you,
clean up any resources you may be using".
That's the crux of it for me anyway. It seems like the simplest
approach is to just adjust my instincts and always make sure the
sequence is fully consumed within the with-open.
Cheers,
Dave
On Wed, Nov 7, 2012 at 10:56 AM, Jim - FooBar(); <jimpil1...@gmail.com> wrote:
I know I'm coming a bit late in this thread but i did not have the chance to
reply earlier...
Can somebody elaborate briefly what is the problem with the combination of
with-open/doseq/line-seq? In a project of mine I'm dealing with files larger
than 200MB (which of course will not even open on a regular text-editor) and
I've been happily using with-open/doseq/line-seq with great success...As
Stuart pointed out as long as the entire processing happens within a
'with-open' all is good and this is the approach I'm always following with
no memory issues...What am I missing? What exactly do you mean by "close the
file"? Do you mean "close the clojure.java.io/reader"? which happens
implicitly when a with-open exits? I've also not understood what the
original problem is...Has anyone had problems with large files?
sorry for the inconvenience...I read the entire thread and I'm still not
understanding!
Jim
On 29/10/12 03:21, Dave Ray wrote:
Stuart,
Thanks for the link. It confirms the suspicions I had about a general
solution for this issue. For the particular code I'm working with,
I'll try pushing with-open further up and see if that gives me some of
the flexibility I'm looking for.
Cheers,
Dave
On Sun, Oct 28, 2012 at 2:21 PM, Stuart Sierra
<the.stuart.sie...@gmail.com> wrote:
On Friday, October 26, 2012 11:11:48 PM UTC-4, daveray wrote:
I guess I looking for a magical line-seq that closes the file correctly
even if you consume part of the sequence, is resilient to exceptions,
etc, etc. I realize that it might be impossible, so I asked. :)
It's been discussed extensively in the past, but no one has come up with
a
solution that adequately solves the general problem. See
http://dev.clojure.org/display/design/Resource+Scopes for examples of
some
attempts.
The best approach I've found is to manage resources like files farther up
the stack. Instead of having a 'with-open' block that returns a sequence,
put the 'with-open' block at a higher level, so that it encompasses the
entire scope in which the file will be used.
-S
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