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From Nathan Bubna <nbu...@gmail.com>
Subject Re: upgrading from 1.5 to 1.7 compatibility issues
Date Mon, 30 Apr 2012 18:05:07 GMT
Can you set velocimacro.context.localscope = true or is it important
for your system to be able to #set global stuff from within macros?

On Mon, Apr 30, 2012 at 10:50 AM, Boris Partensky
<boris.partensky@gmail.com> wrote:
> Thanks Nathan, I think I do get the whole scoping idea, but my
> understanding was that one of the reasons to turn all scoping off by
> default (and have those properties to begin with) was to provide
> backward compatibility - as in: I upgrade to 1.7 and then I start
> turning on all those nice bells and whistles and use scopes and what
> not. Not so seems like? I also find somewhat strange that a a formal
> argument to a macro takes precedence and overwrites a global variable
> with the same name. How would one go about upgrading existing systems?
> We have roughly 1900 macros, big chunk of those are nested... Maybe I
> am misunderstanding something, but this issue makes it almost
> impossible to upgrade (at least for us).
>
>
> Thanks
> Boris
>
> On Mon, Apr 30, 2012 at 12:55 PM, Nathan Bubna <nbubna@gmail.com> wrote:
>> Yeah, it was intended, and part of an overall move toward
>> fixing/simplifying Velocity's variable scoping, avoiding the
>> complexities and costs (performance, yes, but mostly time/brainpower
>> for users and devs alike) of more programming language type behavior.
>> Velocity has long aspired to be a straightfoward template engine and
>> avoid being a complete scripting language.  (Implicit) variable
>> scoping, as seen in 1.5, was seen as a necessary compromise toward the
>> latter; after all, one big fat namespace is always unmanageable,
>> right?  Well, there's ways to make that easy to manage. :)  Let's call
>> it "optional, provided, explicit scoping", explicit because you don't
>> have to grok the contextual scope to understand a reference, optional
>> because you can ignore it, and provided because Velocity does the work
>> of choosing "prefixes" and creating/destroying the scopes (as any
>> implicit scoping system does).  So everything is becoming globally
>> scoped, but it is now trivial to turn on automatic, explicit scopes or
>> namespaces that you can use when you don't want things to live in the
>> global scope.
>>
>> Here's an example...  Do you use $velocityCount to get an index of
>> sorts inside of #foreach directives?  Well, that's an example of mixed
>> implicit/explicit namespacing that gets messy when you nest
>> #foreach's, with no good way to get the parent's count and
>> unwieldiness when you want to add $velocityIndex, $velocityHasNext and
>> so on.  Now, we automatically manage a $foreach var that not only has
>> a 'count' property, but an 'index', 'hasNext', 'parent', and so on
>> (see http://velocity.apache.org/engine/devel/apidocs/org/apache/velocity/runtime/directive/ForeachScope.html).
>>  It also, of course, accepts any property you want to set on it (like
>> any map).  This makes templates instantly understandable, making
>> debugging much better.  You always know exactly what you are referring
>> to, and so does anyone else reading the template.
>>
>> #foreach is the only 'content directive' that has its explicit scope
>> automatically turned on, but all content containing directives
>> (including custom body macros) can have their own explicit,
>> auto-managed scope, named after themselves.  for example, you can flip
>> the macro scope on:
>>
>> macro.provide.scope.control = true
>>
>> and do:
>>
>> #macro( outer $arg )
>>  #set( $macro.arg = $arg )
>>  #inner( 'inner' )
>> #end
>> #macro( inner $arg )
>>  #set( $macro.arg = $arg)
>>  inner: $macro.arg
>>  #if( $macro.parent )outer: $macro.parent.arg#end
>> #end
>>
>> #outer( 'outer' )
>> #inner( 'just inner' )
>>
>> and get
>>
>>  inner: inner
>>  outer: outer
>>  inner: just inner
>>
>> Hope this helps...
>>
>> In any case, there was plenty of thought and discussion that went into
>> this change.  Search http://velocity.markmail.org for 'scope' and you
>> should find more on this.
>>
>> On Mon, Apr 30, 2012 at 8:49 AM, Boris Partensky
>> <boris.partensky@gmail.com> wrote:
>>> Hello, while going through the upgrade I noticed an incompatible
>>> behavior during nested macro evaluation. Looks like in 1.7 (all
>>> default properties) child macro has access to variables set in parent
>>> macro scope (and those take precedence over globals), and 1.5 sees
>>> globals. In the following example, in 1.5 unit test the following
>>> template will evaluate to "globalvar", and in 1.7 - to
>>> "outermacroparam". Is this expected behavior?
>>>
>>>
>>> 1.5 test case
>>>
>>>
>>> public void testVelocityNestedMacroScope() throws Exception
>>>    {
>>>        VelocityEngine ve = new VelocityEngine();
>>>
>>>        ve.init();
>>>
>>>        String template = "#macro(outerMacro $arg1)"+
>>>                          "#innerMacro('blah')"+
>>>                          "#end"+
>>>                          "#macro(innerMacro $arg2)$arg1#end"+
>>>
>>> "#set($arg1='globalval')#outerMacro('outermacroparam')";
>>>        StringWriter eval = new StringWriter();
>>>        boolean b = ve.evaluate(new VelocityContext(), eval, "foo", template);
>>>        assertEquals(eval.toString(), "globalval", eval.toString());
>>>
>>>    }
>>>
>>> 1.7 test case
>>>
>>>
>>>  public void testVelocityNestedMacroScope()
>>>    {
>>>        String template = "#macro(outerMacro $arg1)"+
>>>                          "#innerMacro('blah')"+
>>>                          "#end"+
>>>                          "#macro(innerMacro $arg2)$arg1#end"+
>>>
>>> "#set($arg1='globalvar')#outerMacro('outermacroparam')";
>>>        String eval = evaluate(template);
>>>        assertEquals(eval, "outermacroparam", eval);
>>>
>>>    }
>>>
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