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From "Byron Foster (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 11:13:44 GMT

    [ https://issues.apache.org/jira/browse/VELOCITY-619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12636332#action_12636332
] 

Byron Foster commented on VELOCITY-619:
---------------------------------------

My main motivation for this patch is to provide a need for this functionality when running
in strict mode VELOCITY-618 Mainly it would be good to allow the developer to provide default
values for variables that are referenced but not defined in the template, without the need
to add them to the context in java code.

An alternative to this method would be to provide an exception in strict mode in the case
of #if($foo).  In the case of just a single variable argument in #if strict mode would not
throw an exception in the case $foo is not defined, and the #if would fail. so the following
could be done (As it can be now).

#if ( ! $foo) #set($foo = "bar") #end

My only concern with this is that it is an exception, which means to me a "special case" which
often times leads to confusion in behavior.  But perhaps it's justified in this situation.



> 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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