Re: Odd observation during debugging

On Mon, Jul 16, 2012 at 9:04 AM, Christopher Schultz
<[email protected]> wrote:
> Nathan,
>
> On 7/11/12 1:35 PM, Nathan Bubna wrote:
>> On Wed, Jul 11, 2012 at 9:58 AM, Christopher Schultz
>> <[email protected]> wrote:
>>> Nathan,
>> ...
>>>> See VELOCITY-731 and VELOCITY-692 and others...
>>>
>>> Those were good to read: 1.6 introduced more consistent (if slower)
>>> treatment of references and then a setting was added to get the old
>>> behavior.
>>>
>>> Any idea if a future version of Velocity (maybe 2.x) will have the
>>> default value of that directive set to "false" so that toString will
>>> only be called for users who actually want that?
>>>
>>> While backward-compatibility is certainly a reasonable goal, this
>>> behavior kind of sucks... and I can't really think of too many cases
>>> where it makes sense. Good that there is a setting for it ;)
>>
>> Actually, i still consider it correct for a template language (which
>> is not the same as a scripting language) to treat render-as-empty as
>> false in an #if.  So, my hope for 2.0 was to not to remove that
>> behavior, but to pre-empt it.
>
> On a somewhat related issue, we had been considering using "strict
> reference mode" except that -- at least using the current if-directive
> semantics, it's not practical to do things like this:
>
> #if($mymap && $mymap.containsKey('somekey') &&
> !$mymap.get('somekey').isEmpty() && ...)
>
> ...because many of those individual parts of the predicate may end up
> returning something that is neither Boolean nor a Map, etc. and you
> *must* test them for non-null-ness before trying to use them, otherwise
> you risk an exception.
>
> Without disabling the 'toString' behavior in the configuration, there
> will be no way for these types of checks to execute without spewing lots
> of (in my case) useless String objects (not to mention the wasted time
> to generate them in the first place).
>
> I've seen the use of things like this on occasion:
>
> #if($myobject == $null)
>
> My understanding was that a null reference would never be considered
> equal to *anything*, even another null reference. Does the above
> actually work? And the "$null" is just a reference that is assumed to be
> null, right? When in strict-reference-mode, would that work since $null
> has (presumably) never been defined?

Yes, it works.  And yes, $null is a reference assumed to be null.  And
i believe strict mode is concerned about key existence, so just do:

context.put("null", null);

And you should be able to use that.