Re: [PATCH 5/7] tmp-objdir: new API for creating and removing primary object dirs

[Jeff King <peff@peff.net>]

On Tue, Sep 28, 2021 at 09:22:32PM -0700, Elijah Newren wrote:

> > Not your fault & this pre-dates your patch, but FWIW I prefer our APIs
> > that don't have these "hidden struct" shenanigans (like say "struct
> > string_list") so a caller could just access this, we can just declare it
> > "const" appropriately.
> >
> > We're also all in-tree friends here, so having various accessors for no
> > reason other than to access struct members seems a bit too much.
> 
> That's a fair point, but just to play counterpoint for a minute...
> 
> FWIW, I dislike when our public facing APIs are polluted with all
> kinds of internal details.  merge-recursive being a case in point.
> When writing merge-ort, although I had a struct with public fields,
> that struct also contained an opaque struct (pointer) within it to
> hide several private fields.  (I would have liked to hide or remove a
> few more fields, but couldn't do so while the merge_recursive_options
> struct was shared between both merge-ort and merge-recursive.)
> 
> That said, I agree it can certainly be overdone, and tmp_objdir is
> pretty simple.  However, sometimes even in simple cases I like when
> folks make use of an opaque struct because it means folks put some
> effort into thinking more about the API that should be exposed.
> That's something we as a project have often overlooked in the past, as
> evidenced both by our one-shot usage mentality, and the existence of
> external projects like libgit2 attempting to correct this design
> shortcoming.  I'd like git to move more towards being structured as a
> reusable library as well as a useful command-line tool.

Right, it was definitely a conscious decision to keep the tmp-objdir API
as slim as possible, just because it's such a complicated and confusing
thing in the first place.

For something like a strbuf, giving direct access to the fields makes
sense. Exposing the details of how the struct works (like accessing
".buf" as a NUL-terminated string) are part of its usefulness.

But tmp_objdir represents a more abstract concept, and I wanted to
insulate callers from the details.

That said, the notion of "this is the path of the objdir" is not that
contentious, so I don't mind it too much (but it would be a jump to
exposing the details at all).

-Peff