Re: [PATCH v2 01/10] t: add helper to convert object IDs to paths

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jun 18, 2019, 16:15 UTC
Message-ID: <nycvar.QRO.7.76.6.1906181647480.44@tvgsbejvaqbjf.bet>
In-Reply-To: <c9be7464-21f3-6651-500d-14137f0f1c0f@kdbg.org>

Hi Hannes,

On Tue, 18 Jun 2019, Johannes Sixt wrote:

Show 21 quoted lines

> Am 18.06.19 um 03:29 schrieb brian m. carlson:
> > On 2019-06-17 at 19:05:03, Johannes Schindelin wrote:
> >> I guess it does not *really* matter all that much, but this does spawn a
> >> new process (and I think it actually spawns 4 on Windows, for reasons, and
> >> spawning processes is super expensive on Windows).
> >>
> >> We might actually want to think about using something like this instead
> >> (which admittedly looks a bit like gobbledygook to the uninitiated, but it
> >> definitely avoids any spawned process):
> >>
> >> test_oid_to_path () {
> >> 	echo "${1%${1#??}}/${1#??}"
> >> }
> >
> > I'm fine making that change. The original design was because we had
> > other code that used that technique and I didn't see an obviously better
> > solution. Now you've provided one and a good justification.
>
> Regardless of how it is implemented, I have another gripe with this
> helper: the way it must be used requires a process: $(test_out_to_path
> $foo)

Indeed.

> And looking through this patch series, I see a gazillion of *new*
> process substitutions $(test_something...) and $(basename $whatever).
> Can't we do something about it?

I wish there was. Unix shell scripting has not evolved much in the past, what, 3 decades? So I don't really see a way to "pass variables by reference" to shell functions, short of calling `eval` (which buys preciously little as it _also_ has to spawn a new process [*1*]).

Of course, if we would slowly get away from depending so much on shell scripting, then we would reap quite a few other benefits, too, not only speed, but also much easier debugging, code coverage, etc.

Ciao, Dscho

Footnote *1*: Theoretically, it could be a *ton* faster by using threads on Windows. But threads are pretty much an afterthought on Unix/Linux, so no mainstream POSIX shell supports this. They all `fork()` to interpret an `eval` as far as I can tell.