[Dune-devel] Removing diffOrder in dune-localfunctions will break API

[Oliver Sander]

Dear Dune developers,

I'd like to draw your attention briefly to merge request 63 in the
dune-localfunctions module:

  https://gitlab.dune-project.org/core/dune-localfunctions/merge_requests/63

This merge request removes the diffOrder argument and member of the
LocalBasisTraits class.  It has been a design flaw right from the start,
and removing it has already allowed us (Carsten and me) to simplify
the virtual interface considerably.  The actual removal of diffOrder
is only the last step.

However: removing diffOrder is an API change.  It seems that very few
people have ever actually used it, but if you do then your code will
cease to compile.  We have thought about backward-compatible ways to
remove this, but there is no completely painless way: users of diffOrder
will need to change their code eventually.

The purpose of this email is to warn you about this.  If you think
that you may be affected, please try this merge request to see if it
makes your code fail in ways that are non-trivial to fix.  Part of
the reason why we are attempting a hard break is because we suspect
that it affects only a very small number of people, but we stand
to be proven wrong.  If nobody complains until 1. of November
I will merge the changes into the dune-localfunctions master branch.

Enjoy,
Oliver

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