I think there's an assumption here that requires/provides would be
added on the class (or trait) tag level. My understanding/assumption
has been that requires/provides would be on the library (or module)
level -- perhaps a separate tag that would be valid only within
library (or module) declarations:
<library>
<requires tag="swf8"/>
<provides tag="SWFVisualEffects"/>
...
</library>
This, in combination with the <switch> tag that Henry recently
resurrected would give us sufficient flexibility to handle runtime-
specific features, I think.
jim
On May 5, 2006, at 4:24 PM, Max Carlson wrote:
> There has been a lot of discussion around adding requires/provides to
> the platform to ease development around runtime-specific features.
> Classes would be able to say they provide certain feature(s). Other
> classes could require those features, and the compiler would warn if a
> required feature was not available.
>
> One issue with the existing proposal is it doesn't make adding
> runtime-specific features to existing base classes, (like view) easy.
> At first blush this doesn't seem so bad.
>
> Imagine adding Flash 8 visual effects. With the proposed mechanism
> developers create a subclass of view that provides a feature, say
> 'SWFVisualEffects' which in turn requires 'swf8.' The fact
> 'SWFVisualEffects' can only be added to a subclass of view has all
> sorts
> of ramifications to component hierarchies and the like, because
> components that want to take advantage of new features now.have to
> extend the new class instead just extending view (like they do
> already).
>
> Ideally we provide a mechanism that allows developers to mix features
> into existing base classes while still providing warnings where
> they're
> unsupported. This could be accomplished by using a variant of traits
> that supports requires/provides. Right now, adding SWFVisualEffects
> would require hacking the swf kernel directly and adding the feature
> into view. This is fine, but it also requires manually adding with
> warnings for unsupported (non-swf) runtimes.
>
> Because of this, I don't think class-based requires/provides gets us a
> lot of mileage unless it somehow supports mixing into existing base
> classes (while still providing warnings for non-supported runtimes).
>
> For now, we already have conditional compilation for the kernel
> with 'if
> ($runtime)' conditionals. Adding requires/provides into traits could
> provide a much safer (and much more useful) way for developers to add
> runtime-specific features to the various kernels. This would
> provide a
> mechanism that automatically warns when a developer requires features
> that aren't provided/available, while saving developers from manually
> writing warnings for other runtimes.
>
> What are your thoughts?
>
> --
> Regards,
> Max Carlson
> OpenLaszlo.org
> _______________________________________________
> Laszlo-dev mailing list
> [email protected]
> http://www.openlaszlo.org/mailman/listinfo/laszlo-dev
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