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From Guillaume Polet <guillaume.po...@gmail.com>
Subject VelocityMacro scope
Date Thu, 20 Oct 2011 12:41:22 GMT
Hi List,

it's been a while since I wrote here (at least a few years), mainly 
because I had not too much trouble resolving my issues myself but this 
time I am kind of stuck.
We recently upgraded from Velocity 1.6.2 to velocity 1.7 and we 
encountered a lot of issues. While I managed to fix most of them, there 
is an important one that I can't get passed.

Simplifying my code, here is a little snippet that used to work:
#macro(foo $bar)
     #set($bar = 100)
#end

#set($xyz = 0)
Before: $xyz
#foo($xyz)
After: $xyz

Basically, we pass a variable to a macro, and setting the value of the 
variable in the macro impacted the passed argument, ie, the output we 
used to have in 1.6.2 was:
Before: 0
After: 100
Now, in velocity 1.7, I get the following:
Before: 0
After: 0

This is of course a really strong change of behaviour but ok I guess 
there might be some good reason for that (although I think it kind of 
contradicts what the doc says about velcoity macro arguments since it 
says that the passed argument is re-evaluated each time it occurs in the 
VM, in my opinion, I feel that $bar should resolve to $xyz, and 
therefore the #set would set the value of $xyz. The whole point of doing 
that is to be able to return a value (or even several values) from a macro).

Now, the weirdest thing, I believe is, if you change the name of the 
passed argument to $bar:
#macro(foo $bar)
     #set($bar = 100)
#end

#set($bar= 0)
Before: $bar
#foo($bar)
After: $bar

Then I get what I used to have, ie:
Before: 0
After: 100

I feel like this is really mixing things up. Either the value can 
propagate from the macro to the calling-level, either it should be 
prevented. But have a mix of both of them is really not predictable nor 
robust. If by any chance, I happen to call my argument the same way it 
is called in the macro, the behaviour of the template is completely 
changed. I would assume that the name of a variable should not matter on 
both sides. I should be able to rename $bar to $bar123 without noticing 
any change and the same goes for $xyz which could be either $xyz or $bar 
without modifying the outcome. Or is this just me?
Personnally, I am in favour of the first behaviour.

Now, my question would be, how can I achieve the behaviour observed in 
1.6.2 with velocity 1.7, or what technique can I use to return values 
from a velocity macro?

If you wonder why I am trying to that instead of moving my code to Java 
classes, the reason is that I heavily rely on templates to generate all 
kinds of stuff (full web-application, Latex documents, DocX documents, 
etc...) but I also allow the user of my application to modify those 
templates at runtime without needing to know anything about classes, 
Java code, etc... I can get somebody started on VTL in 5 minutes while 
it would take me days to get him started with Java.

Thanks very much in advance,

Guillaume


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