Error handling in the constructor of a VMOD object

[Carlos Abalde]

Hi all,

I'm looking for advise / best-practices related to VMODs, objects and 
their __init() constructors. Let's assume a foo VMOD and a VCL like this 
one:

import foo;

sub vcl_init {
   new myfoo = foo.instance(...);

   ...
}

What's your suggestion to handle errors in the constructor? So far my 
approach is returning a NULL pointer if for some reason the instance 
cannot be created, which IMO is good enough because that way execution 
of 'vcl_init' will continue (meh...), but in the end it will fail (with 
a slightly obscure error), and then the VCL won't be loaded. However, in 
such a scenario ans using that strategy, a VCL like this one would 
trigger a panic:

sub vcl_init {
   new myfoo = foo.instance(...);
   myfoo.whatever(...);

   ...
}

Transforming all VMOD methods in no-ops when the received pointer is 
NULL could be an option, but it looks ugly. I guess another option would 
be to add a '.isnull()' method to the object and then use it in 'vcl_init':

sub vcl_init {
   new myfoo = foo.instance(...);
   if (myfoo.isnull()) {
     return (fail);
   }

   myfoo.whatever(...);

   ...
}

My doubt is if I'm missing something and a better approach already 
exists for error handling during 'vcl_init'. Any suggestion?

Thanks,

-- 
Carlos Abalde
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