While-like structure in Velocity?
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
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Re: While-like structure in Velocity?
#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. Even if the queue is materialized by a linked list rather than by an array? #foreach over a linked list is the way to go, I think. Claude - To unsubscribe, e-mail: user-unsubscr...@velocity.apache.org For additional commands, e-mail: user-h...@velocity.apache.org
Re: While-like structure in Velocity?
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..10])
#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
--
Sergiu Dumitriu
http://purl.org/net/sergiu
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