Re: "While"-like structure in Velocity?

Sergiu,

On 5/15/13 3:04 PM, Sergiu Dumitriu wrote:
> On 05/15/2013 12:11 PM, Christopher Schultz wrote:
>> All,
>>
>> I've searched the archives for "while" capabilities in Velocity, and
>> mostly the answers have been things like "that's beyond the scope of
>> Velocity... you want a real programming language for that".
>>
>> I'd like to do something that naturally would use a while loop, but
>> perhaps someone can offer an alternative suggestion.
>>
>> I need to traverse a queue, but that queue needs to be able to modify
>> itself during the processing. Basically, something like this:
>>
>> while (!queue.empty) {
>>   // do something with the head element
>>   // possible enqueue some more items at the back
>> }
>>
>> #foreach would be the way to do it if the queue didn't have to be
>> modified, but I'll get an exception if I try to traverse an iterator
>> over the queue and then modify it mid-flight.
>>
>> Right now, I have this written as a JSP but I'd rather have it as a
>> Velocity template.
>>
>> My only thought is to create an ugly class that implements Iterator and
>> wraps the queue but is much less strict than a standard iterator. Any
>> suggestions?
>>
>> -chris
>>
> 
> While not a very clean solution, you can use a very large foreach and
> manually work with the queue inside the loop, and #break($foreach) once
> the queue is empty:
> 
> #foreach($i in [0..100000])
>   #if ($queue.isEmpty())
>     #break($foreach)
>   #end
>   #set ($item = $queue.pop())
>   ## Do stuff with $item
>   #if (should add more things)
>     #set ($discard = $queue.add(new things))
>   #end
> #end

That's actually a great suggestion. I've never used "break" in a foreach
loop before. $foreach becomes the loop-control identifier for #break?

I'll give that a try. 10,000 seems completely reasonable given that (for
now) I'll never really have a queue that grows to a size more than about
5000, even in the most pathological case.

Thanks,
-chris

-----BEGIN PGP SIGNATURE-----
Version: GnuPG/MacGPG2 v2.0.17 (Darwin)
Comment: GPGTools - http://gpgtools.org
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQIcBAEBCAAGBQJRlPoKAAoJEBzwKT+lPKRYSTEP/24TBokeDQ6vnutO7ZVd4ihL
wh5AISwqY4S9YBQiNFJ8qK3MsEjL3Cgby7QmRdZFCuj97BmMT9bDmBI8ojJ4w1xJ
6+KRd1TAOIzEaEOY42Vh5p+Nrut/MD1mMgxOj+nzBceLwqVHqlQqG01WePzTM2Ib
+jVbDum5wUCstOaWo9QetrzXKP3GvaFHBOSUlLuMxnGN/BMLN2fIZCKkNz6CFv31
qMLU/qGqseAnc2BkyTNAVs9j0GigCr30X8CxycootVRZ1pEUvSpJrgkqU4w9POCa
nY2ciKy7d3zPz1qJD0+ZyhvvzpNnfcHKB0vIcuMywgpvC5Kdym9FPASBfzF4Oab+
MLAiBS9PzHUbIKCtkINmmpnSYbUQrljXut9kcIF0rA01phHzAyF1j8P95GdOLhyU
IvxCjqZ5djH7286H95FyI1wyAyW2j5ZaUY6PnSPqtLg1+PqGyrpp6GEb2DrxSlyV
xwG0moXm72pcLaapl9Wgjl/PAHUuSqgrp7oOgrfTRYY5GsMpXyOy5tzNJf53Sq1p
+ICMU7qJQ5eWCrpoQ7BdBddfHKTDcqY8pRTNqbURKyn3udC4gPOqq6RrWi0QMotJ
73FbXdG+ab0FQmrRHNCH2cZlCmNAomLAPa0l7E019Mo0FOoC60vZJI8YPm3kNkGK
Fso1ulHN1G7VDauzxfnx
=IYAI
-----END PGP SIGNATURE-----