From: Christian Couder <chriscool@tuxfamily.org>
Date: Fri, 14 Feb 2014 21:41:33 GMT
Subject: Re: [PATCH v5 02/14] trailer: process trailers from file and arguments
Message-ID: <20140214.224133.484636406629780362.chriscool@tuxfamily.org>
In-Reply-To: <xmqqa9dxr09k.fsf@gitster.dls.corp.google.com>

From: Junio C Hamano <gitster@pobox.com>
>
> These numerous questions you have to ask are indications why
> choosing "this condition goes to the left hand side of the equal
> sign (e.g. exists)" and "this condition goes to the right hand side
> (e.g. do-this-if_neighbor)" is not working well.  The user has to
> remember which conditions go to the variable name and which
> conditions go to the action part.

If we limit it to "if_exists" and "if_missing", the user can remember
that without things becoming too complex.

> That is, not splitting the logic into two parts like you did,
> i.e. "if_X = do_Y_if_Z", which invites "why is it not if_true =
> do_Y_if_X_and_Z, if_X_and_Z = do_Y, if_Z = do_Y_if_X"?

It perhaps invite it, but there are reasons why splitting the logic
too much is not a good idea and why limiting the split to "if_exists"
and "if_missing" is a good tradeoff.

> One possible way to avoid the confusion is to say "do_Y_if_X_and_Z"
> without making the rule split into conditions and actions---I am
> NOT saying that is _better_, there may be other solutions to avoid
> this two-part logic in a cleaner way.

This has been discussed first last November and I don't think that a
solution better than what I implemented has been suggested.

The problem is we not only want to say:

    action = do_Y_if_X_and_Z

but we also want to say:

    action = do_Y_if_X_and_Z AND do_U_if_V

For example some people might want:

    if_exists = overwrite
    if_missing = add

while others might want:

    if_exists = overwrite
    if_missing = do_nothing

and I don't see how we can say that with just:

    action = do_Y_if_X_and_Z

Thanks,
Christian.