[petsc-dev] We need to cleanup viewers

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
>    The problem is that many viewers call viewers on inner objects
>    recursively. Under the old system if ANY of the inner objects, no
>    matter how freaking trivial did not support the users viewer BOOM
>    end of program with error message. Very annoying. For all objects
>    writing “empty” routines that just return for each and every
>    possible viewers is impossible and never kept up to date. Hence the
>    current model which is not confusing at all if users understand
>    that not all objects respond to all viewers.

In those cases, could the top level flag those viewers as optional
before passing it down to lower levels?

>    I would be very happy to see the viewers handled properly with a
>    double dispatch system. But that system needs to be designed and
>    evaluated. I wrote this sentence because I would be very happy if
>    you wrote a proper double dispatch system for viewers that passes
>    our satisfactory requirements. I just don’t want a half-assed
>    crappy confusing 1 1/2 dispatch system that sucks.

I'll experiment with this after the release.
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