Re: [Question] Can git cat-file have a type filtering option?

[Junio C Hamano <gitster@pobox.com>]

ZheNing Hu <adlternative@gmail.com> writes:

> all blobs, and then use `git cat-file --batch` to retrieve them. This
> is not very elegant, or in other words, it might be better to have an
> internal implementation of filtering within `git cat-file
> --batch-all-objects`.

It does sound prominently elegant to have each tool does one task
and does it well, and being able to flexibly combine them to achieve
a larger task.

Once that approach is working well, it may still make sense to give
a special case codepath that bundles a specific combination of these
primitive features, if use cases for the specific combination appear
often.  But I do not know if the particular one, "we do not want to
feed specific list of objects to check to 'cat-file --batch'",
qualifies as one.

> For example, `--type-filter`?

Is the object type the only thing that people often would want to
base their filtering decision on?  Will we then see somebody else
request a "--size-filter", and then somebody else realizes that the
filtering criteria based on size need to be different between blobs
(most likely counted in bytes) and trees (it may be more convenient
to count the tree entries, not byes)?  It sounds rather messy and
we may be better off having such an extensible logic in one place.

Like rev-list's object list filtering, that is.

Is the logic that implements rev-list's object list filtering
something that is easily called from the side, as if it were a
library routine?  Refactoring that and teaching cat-file an option
to activate that logic might be more palatable.

Thanks.