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From "Christoph Reck (JIRA)" <...@velocity.apache.org>
Subject [jira] Commented: (VELOCITY-619) New set modifier so that set only assigns a value when variable is not defined.
Date Thu, 02 Oct 2008 08:27:44 GMT

    [ https://issues.apache.org/jira/browse/VELOCITY-619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12636300#action_12636300
] 

Christoph Reck commented on VELOCITY-619:
-----------------------------------------

True that if someone used #set( $!foo = $bar ) in an earlier version it set the value ignoring
the bang. At some point it was discussed to use this syntax to explicetely allow setting a
NULL value. Changing this would break BC (even though it is an unimplemented feature - some
people may have local patches to do so - as I had once...).

I propose to add a new directive for this, instead of overloading the #set with bang to mean
"set only if undefined".
Possible directive names: #default, #option, #setUndefined, #setIfUndefined, #allow, #let

P.S. This is inline with some new directives introduced in Vel1.6: #evaluate, #define($ref)...#end,
and #break

> New set modifier so that set only assigns a value when variable is not defined.
> -------------------------------------------------------------------------------
>
>                 Key: VELOCITY-619
>                 URL: https://issues.apache.org/jira/browse/VELOCITY-619
>             Project: Velocity
>          Issue Type: Improvement
>          Components: Engine
>            Reporter: Byron Foster
>         Attachments: setBangModifier_2.patch
>
>
> Define a new #set modifier such that a variable is only set if it is not defined, like
so:
> #set($!foo = "bar")
> If the '!' character proceeds the variable foo, then $foo will be set with the value
of "bar" ONLY IF $foo is not defined (is not in the context).  Otherwise if $foo is defined
it will remain unchanged.

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