Re: Multiple types

The type-system of FTL (for FreeMarker Template Language) corresponds
to the TemplateMoldel interfaces. Since a class can implement several
interfaces at once, you have multi-typing. Like, TemplateNumberModel
plus TemplateHashModel, an instance of that class will be both a
number and a hash for FTL. So creating multi-typed values is trivial
as you see, however it's something that you do outside the templates
(there is no FTL operator or literal to create a multi-typed values).

Unfortunately, I'm afraid you are out of luck with macros, however.
I'm not the author of the FM code-base so possibly I miss something...
but most probably I don't. So the problem is that as far as the public
API is concerned, macros is a mess in FM. (Maybe because they are
ancient pre-TemplateModel constructs... I don't know). A macro is an
instance of freemarker.core.Macro, which is a final class, not an
interface. Plus, calling a macro in Java through a Macro object
requires you to access the freemarker.core.Environment.visit(Macro,
...etc) method, which is not a public method. Thus, as far as I see,
you just can't mix TempalateHashModel in for purely technical reasons.
So unless using TemplateDirectiveModel-s or TemplateMethodModel-s
instead of macros works for you, you are out of luck.


Sunday, June 27, 2010, 12:49:50 PM, Alex Robinson wrote:

> I note this in the documentation:
>
> "A value can have multiple types at the same time, although it's
> rarely utilized"
> 
> http://freemarker.sourceforge.net/docs/dgui_datamodel_basics.html#autoid_13
>
> However I don't understand how it's actually possible to use.
>
> I'm interested in this feature (at first read I dismissed it as scary)
> since it would allow me to group macros like
>
>    macro1, macro1.submacro1
>
> rather than
>
>    macro1, macro1Submacro1
>
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-- 
Best regards,
 Daniel Dekany


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