NAME

       Template::Alloy::Velocity - Velocity (VTL) role

DESCRIPTION

       The Template::Alloy::Velocity role provides the syntax and the interface for the Velocity Templating
       Language (VTL).  It also brings many of the features from the various templating systems.

       See the Template::Alloy documentation for configuration and other parameters.

       The following documents have more information about the velocity language.

           http://velocity.apache.org/engine/devel/vtl-reference-guide.html
           http://www.javaworld.com/javaworld/jw-12-2001/jw-1228-velocity.html?page=4

TODO

       Add language usage and samples.

ROLE METHODS

       "parse_tree_velocity"
           Used bh the parse_tree method when SYNTAX is set to 'velocity'.

       "merge"
           Similar to process_simple, but with syntax set to velocity.

UNSUPPORTED VELOCITY SPEC

       •   The  magic  Java  Velocity  property lookups don't exist.  You must use the actual method name, Alloy
           will not try to guess it for you.  Java Velocity  allows  you  to  type  $object.Attribute  and  Java
           Velocity  will  look  for  the  Attribute,  getAttribute, getattribute, isAttribute methods.  In Perl
           Alloy, you can call $object.can('Attribute') to introspect the object.

       •   Escaping of variables is consistent.  The Java Velocity spec is not.  The  velocity  spec  says  that
           "\\$email" will return "\\$email" if email is not defined and it will return "\foo" if email is equal
           to "foo".  The slash behavior magically changes according to the spec.  In Alloy the "\\$email" would
           be "\$email" if email is not defined.

       •   You  can  set items to null (undefined) in Alloy.  According to the Java Velocity reference-guide you
           have to configure  Velocity  to  do  this.   To  get  the  other  behavior,  you  would  need  to  do
           "#if($questionable)#set($foo=$questionable)#end".   The default Velocity spec way provides no way for
           checking null return values.

       •   There currently isn't a "literal" directive.  The VTL reference-guide doesn't mention  #literal,  but
           the user-guide does.  In Alloy you can use the following:

               #get('#foreach($a in [1..3]) $a #end')

           We  will  probably  add the literal support - but it will still have to parse the document, so unless
           you are using compile_perl, you will parse literal sections multiple times.

       •   There is no "$velocityCount" .  Use "$loop.count" .

       •   In Alloy, excess whitespace outside of the directive matters.  In the VTL user-guide it mentions that
           all excess whitespace is gobbled up.  Alloy supports the TT chomp  operators.   These  operators  are
           placed just inside the open and close parenthesis of directives as in the following:

                #set(~ $a = 1 ~)

       •   In  Alloy, division using "/" is always floating point.  If you want integer division, use "div".  In
           Java Velocity, "/" division is integer only if both numbers are integers.

       •   Perl doesn't support negative ranges.  However, arrays do have the reverse method.

                #foreach( $bar in [-2 .. 2].reverse ) $bar #end

       •   In Alloy arguments to macros are passed by value, not by name.  This is easy to achieve with alloy  -
           simply  encase  your  arguments  in  single  quotes and then eval the argument inside the macro.  The
           velocity people claim this feature as a jealously guarded feature.  My first template system "WrapEx"
           had the same feature.  It happened as an accident.  It represents lazy software architecture  and  is
           difficult to optimize.

AUTHOR

       Paul Seamons <paul@seamons.com>

LICENSE

       This module may be distributed under the same terms as Perl itself.

perl v5.36.0                                       2022-10-16                     Template::Alloy::Velocity(3pm)