Re: [PATCH 2/2] [GSOC][RFC] ref-filter: introduce enum atom_type

From: ZheNing Hu <adlternative@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Christian Couder <christian.couder@gmail.com>,
	ZheNing Hu via GitGitGadget <gitgitgadget@gmail.com>,
	git <git@vger.kernel.org>, Jeff King <peff@peff.net>,
	Christian Couder <chriscool@tuxfamily.org>,
	Hariom Verma <hariom18599@gmail.com>
Subject: Re: [PATCH 2/2] [GSOC][RFC] ref-filter: introduce enum atom_type
Date: Sun, 9 May 2021 21:44:58 +0800	[thread overview]
Message-ID: <CAOLTT8Q3QLsD=yy8OBYcHh7FGhfmOebLVk71fidoih-X5HgNsQ@mail.gmail.com> (raw)
In-Reply-To: <xmqqh7jctiru.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> 于2021年5月9日周日 下午4:26写道：
>
> Christian Couder <christian.couder@gmail.com> writes:
>
> > I am not sure it's worth having an atom_type field for each valid_atom
> > element if the value of that field is already the index of the
> > element, because then one would always be able to replace
> > `valid_atom[i].atom_type` with just `i`. Or is it for some kind of
> > type safety issue?
>
> > I wonder if the enum should be instead defined like this:
> >
> > enum atom_type {
> > ATOM_UNKNOWN = 0,
> > ATOM_REFNAME,
> > ...
> > ATOM_ELSE,
> > ATOM_INVALID, /* should be last */
> > };
> >
> > As a struct containing an atom_type would typically be initialized
> > with 0 after being allocated, `ATOM_UNKNOWN = 0` could ensure that we
> > can easily distinguish such a struct where the atom_type is known from
> > such a struct where it is unknown yet.
> >
> > Having ATOM_INVALID as always the last enum value (even if some new
> > ones are added later) could help us iterate over the valid atoms using
> > something like:
> >
> > for (i = ATOM_UNKNOWN + 1; i < ATOM_INVALID; i++)
> >         /* do something with valid_atom[i] */;
>
> OK.
>
> As to "safety", I think it still makes sense to declare "enum", but
> I agree that we do not necessarily have to have it in the valid_atom[]
> struct.  We could do something like this instead:
>
>     static struct {
>             const char *name;
>             info_source source;
>             cmp_type cmp_type;
>             int (*parser)(const struct ref_format *format, struct used_atom *atom,
>                           const char *arg, struct strbuf *err);
>     } valid_atom[] = {
>            [ATOM_REFNAME] = { "refname", SOURCE_NONE, FIELD_STR, refname_atom_parser },
>            [ATOM_OBJECTTYPE] = { "objecttype", SOURCE_OTHER, FIELD_STR, objecttype...
>            [ATOM_OBJECTSIZE] = { "objectsize", SOURCE_OTHER, FIELD_ULONG, objectsi...
>            ...

Thank! Good suggection. We hope that the atom_type and
valid_atom items establish a clear connection. Maybe we
should add some comments before the definition of the
`enum atom_type` to remind the coder of the connection
between atom_type and valid_atom.

--
ZheNing Hu