[jira] Commented: (VELOCITY-704) VTL Simplicity - "Control" objects

["Nathan Bubna (JIRA)" <de...@velocity.apache.org>]

    [ https://issues.apache.org/jira/browse/VELOCITY-704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12674787#action_12674787 ] 

Nathan Bubna commented on VELOCITY-704:
---------------------------------------

We could give nested controls access to their parent of the same type like this:

#foreach( $item in $list )
  #foreach( $attr in $item.attributes)
    #if( $attr == $null ) $foreach.parent.stop() #end
    ${foreach.parent.count}.${foreach.count}: $attr
  #end
#end

No need to do the #set( $outer = $foreach ).

I'm also thinking that we may be able to start introducing these control objects in 1.x.  This could allow us to start deprecating the replaced features (#stop, #break, $velocityCount, $velocityHasNext, macro localscope setting) prior to 2.0.   Given my frustrating and continuing experience with VelocityTools 2.0, i would like 2.0 to be as clean of deprecations as possible, and not try hard to maintain compatibility for 1.x.  Better to start the transition in 1.x wherever reasonable.

> VTL Simplicity - "Control" objects
> ----------------------------------
>
>                 Key: VELOCITY-704
>                 URL: https://issues.apache.org/jira/browse/VELOCITY-704
>             Project: Velocity
>          Issue Type: New Feature
>          Components: Engine
>            Reporter: Nathan Bubna
>             Fix For: 2.0
>
>
> In the discussion for VELOCITY-680, Claude suggested the addition of what i'm calling "control" objects as a solution.   These would have the same name as the block directive or macro to which they belong.    At a minimum, these would provide get(key), set(key, value) and stop() methods to control the reference scoping and execution of the block to which they belong.   Directives could extend the basic control object to provide additional functions, such as index() and hasNext() for #foreach.   Here's some examples:
> #foreach( $user in $users )
> $user#if( $foreach.hasNext ), #end
> #if( $foreach.count > 10 ) $foreach.stop() #end
> #end
> #macro( foo $bar )
> blah blah #if( $bar == 'bar' ) $foo.stop() #end
> #set( $foo.woogie = 'woogie' )
> $foo.woogie
> #end
> #foreach( $item in $list )
>   #set( $outer = $foreach )
>   #foreach( $attr in $item.attributes )
>     #if ( $attr == $null ) $outer.stop()#end
>   #end
> #end
> ------foo.vm---------
> blah blah $template.stop() blah
> ------------------------
> #define( $foo )
> blah blah $define.stop() blah
> #end
> This could allow us to greatly simplify all sorts of things.  We could remove the #break, #stop and #return directives.  We would no longer need to have "local" contexts for foreach loops or macros; instead users could set and get local variables directly in the provided namespace.   All else would be global.   This may even cut down our internal code complexity a fair bit.  It'll certainly obviate the need for several configuration properties and internal contexts.  Everything becomes much more explicit, obvious and robust.   I also don't think it looks ugly. :)
> We would, of course, have to make sure that the StopExceptions thrown by stop() aren't wrapped into MethodInvocationExceptions.  We'd have to make the directives clean up their control when done rendering, and if they're nested in a directive of the same type, then they should save and restore the reference to the parent control.   We'd also have to figure out a good default name to give the control objects for the top-level control object, and whether it would be different than the name of the control object used during a #parse call.  $template?  $parse?  $velocity?  If we wanted to use $template--which i think works well for both top-level and #parse--then we'd probably have to make it configurable, since that's likely to conflict.   And if we make that configurable, i suppose we may as well make it configurable for the others too.
> I'm struggling to think of any real downside to this.  Most of the replaced features (implicit macro localscope, #stop, #break, $velocityHasNext) are either not default behavior or are new features.  I'd wager that most people would only have to change $velocityCount to $foreach.count.  Even that's no big deal, since this would be for a major version change.  , The worst i can think of is the fact that for a couple of these controls it would mean a few more keystrokes.  Considering all the gains in extensibility, explicitness and simplification (for us and users), i think it's worth a few keystrokes.
> What do you guys think?

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