Re: instanceOf and/or isAssignableFrom operator in freemarker

Wednesday, April 22, 2009, 8:49:41 PM, dlevancho wrote:
>
> Hi,
>
> I am trying to find a way to test if a certain object implements certain
> Interface, or at lease if it is instance eof certain class,but as I
> understand freemarker does not support that operator?

It doesn't. I mean, not out-of-the-box. The template language (FTL)
doesn't even know the idea of classes, it only has numbers, string,
boolean, hashes, sequences, and a few more such basic types. Actually,
this issues is pretty clearly data-model related (certain entries in
the data-model should be able to tell if they are a YouKnowWhat).

> I would low to see a isAssignableFrom check or at least instanceOf
> operator, but so far I have not seen a word mention about them in
> freemarker manual . can anyone help me out with a workaround?

For now, you can either write a TemplatMethodModel for it, or extend
the object wrapper (BeansWrapper). Or, maybe you can use duck-typing.
I believe this is pretty clearly a data-model issue, and as such I
would advise to solve it be customizing BeansWrapper (see also:
Configuration.setObjectWrapper).

Actually, Attila, can't BeansWrapper already do that? I don't know...
I guess it should be able to, given it *is* for exposing Java object
as-is (OK, with some security restrictions and like, but you get what
I mean), and the class is a quite important information for Java
classes, given that in the Java world duck-typing and like is at best
rare.

-- 
Best regards,
 Daniel Dekany


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