[stringtemplate-interest] Group Syntax extension for ModelAdapter and Renderer

[Udo Borkowski]

The "propagation" approach solves one half of the problem: with this approach one could use renderers and adapters in groups that are imported through the "import" statement (and not programmatically). This is currently not possible.

But the other half of the problem still exists: assume I change a group G and use some special renderer in the new version. The group G is imported by many other groups (maybe indirectly). I now need to find all the "roots" of imports to G and add the new renderer there. This can really become a maintenance nightmare. Providing the "renderer" syntax extension and defining the renderer in the group text would solve this issue.

Regarding the implementation of the "propagation" approach: registering a renderer will require to visit all directly and indirectly imported groups and add the renderer to all of them, possibly creating new maps etc.. Most of the times this will be extra work as the imported groups don't reference that renderer. Propagating a renderer to all imported groups may lead to a performance issue when using large systems.

I would also hesitate to use the "propagation" approach as it adds a new concept to StringTemplate ("propagation of renderers") that in addition seems to "reverse" an already existing concept ("inheritance"). I guess this may to misunderstandings. 

In contrast to this the "renderer" syntax extension does not use a new concept but rather makes an existing feature ("registerRenderer") accessible to those users who prefer to work on the group text than coding in Java.

As the "propagation" approach does not solve the whole problem I still think we should add the "renderer"/"adapter" feature I suggested.

Udo

P.S.: all stuff mentioned regarding "renderer" also applied "adapter".



On 23.06.2011, at 23:38, Sam Harwell wrote:

> This is an interesting problem. Normally when things are inherited, they start at the imported group and propagate to the group that imported them. In this case, it sounds like you want to propagate it from the topmost group to all the groups it imports.
>  
> Perhaps the thing to do here is propagate renderers to groups imported with STGroup.importTemplates(Token) (those are the ones imported via the group file), but don’t propagate them to groups imported with a direct call to importTemplates(STGroup)?
>  
> If you look at the diff of TemplateGroup.cs in CL8734 (it’s a small diff), you can see how I adjusted the import code to handle the unload() method in everyone’s cases. If the java code is adjusted in the same way (I can make the change if you want), then it’s easy to propagate renderers by the following two rules:
>  
> 1.       When STGroup.importTemplates(Token) is called, the current group’s renderers are added to the group that just got imported. This handles the case where the renderer is registered before the group is imported (especially relevant in reloading a group file after calling unload()).
> 2.       When a renderer is added to a group, it is automatically added (by calling registerRenderer) to all groups in the importsToClearOnUnload list. This handles the case where the group is imported before the renderer is registered.
>  
> Sam
>  
> From: stringtemplate-interest-bounces at antlr.org [mailto:stringtemplate-interest-bounces at antlr.org] On Behalf Of Terence Parr
> Sent: Thursday, June 23, 2011 1:44 PM
> To: Udo Borkowski
> Cc: stringtemplate-interest Template
> Subject: Re: [stringtemplate-interest] Group Syntax extension for ModelAdapter and Renderer
>  
> I think that we should probably keep this at the programming level.   should we make renderers inherited instead to solve your problem?
>  
> Ter
> On Jun 21, 2011, at 1:17 AM, Udo Borkowski wrote:
> 
> 
> Hi,
>  
> currently we programmatically register ModelAdapters and Renderers to an STGroup.
>  
> What about providing an extension to the syntax of Group to also define these in a Group file?
>  
> E.g. I could imagine to use something like
>  
> adapter "org.w3c.dom.Node" "com.collinfagan.strum.adapters.xml.NodeModelAdapter"
> renderer "org.w3c.dom.Node" "com.collinfagan.strum.adapters.xml.NodeRenderer"
>  
> at the top of an Group file. This would mean the same as running this Java code for the group:
>  
> group.registerRenderer(org.w3c.dom.Node.class, new com.collinfagan.strum.adapters.xml.NodeRenderer());
> group.registerModelAdaptor(org.w3c.dom.Node.class, new com.collinfagan.strum.adapters.xml.NodeModelAdapter()); 
>  
> Especially when importing groups this feature comes in handy as I cannot register adapters/renderers when importing. In these cases I must rely on the root group. For this group R we must register ALL adapters/renders used in ANY group R imports. This make things hard to maintain as using a "new" renderer in some template T requires me to add the "registerRenderer" in EVERY code using T, maybe indirectly through imports.
>  
> Similar to features discussed earlier this feature is easy to implement for the STGroupFile, but the STGroupDir currently has no proper place to hold this information. So we may also need to tackle this re-appearing topic, too.
>  
>  
> What do others think?
>  
> Udo
>  
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>  

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