[stringtemplate-interest] template existence testing

[Zenaan Harkness]

On Sat, Mar 29, 2008 at 01:07:25PM -0700, Terence Parr wrote:
>
> On Mar 29, 2008, at 5:43 AM, Zenaan Harkness wrote:
>> Hi, I've come across a feature which I would find useful:
>>
>> It might sound odd, but I would like to be able to, within an <if(...)>
>> block, test for the existence of a specific template name.
>>
>> I need to provide template-level specialization of getter/setter method
>> bodies, and I'd like the template name to be tested for automatically in
>> the if block, so that a default method body is used normally, and the
>> specialization is used otherwise.
>
> Wouldn't normal group inheritance handle this case?

For inheritance to work, I would have to have an empty get-, set- and
misc- template in a parent group, for _every_ conceivable attribute that
my model might want to model, which is simply silly.

The attributes of a particular model, a farm let's say, might be
land-size, water-flow, crops, etc, whereas a model of a music album
would have artist, recording company and track attributes. My views
cannot possibly guess the attributes desired by my models (and the
models are totally separate).

So the thing is, I want, on occasion, to have a specialization of say, a
Java Bean view template, and I have in this actual example, attributes
of att-version-major, att-version-minor, and att-version. Now
att-version is in my current implementation, to be rendered as a
concatenation of the major and minor version strings, so I want, instead
of a normal "return _attVersion;" getter for att-version, a
specialization (in a one-shot sub-template), where att-version's getter
body is specialized into "return _attVersionMajor + _attVersionMinor;".

Since there are three attributes, how does my standard javaBean
template's getterBody(att)... template know that the sub-template-group
wants to override that _particular_ attribute's getter method body and
leave the other two as standard getters?

I can already see many other uses for such template specialization,
where the specialization is per-model-attribute, where the model
attribute is entirely unknown in advance, and the polymorphic
sub-template-group feature of StringTemplate would otherwise very
cleanly solve this problem, if I could only test for the existence of a
particular template (in the sub group), the name of which is unknown in
advance, but should be used if it exists.


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