Re: [PATCH 1/2] pkt-line: fix declaration of `set_packet_header()`

From: Junio C Hamano <gitster@pobox.com>
Date: May 16, 2019, 02:24 UTC
Message-ID: <xmqq36lf5e7a.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <nycvar.QRO.7.76.6.1905151234370.44@tvgsbejvaqbjf.bet>

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

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>> lacked the "const" for that reason, but apparently some compilers
>> complain about the parameter type mismatch.
>
> We could be more explicit, as we know exactly that it is MS Visual C 2017
> that is complaining.

We could be, but I do not see a point of shaming one particular compiler vendor.

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>> Let's squelch it by removing the "const" that is pointless for a
>> small function like this, which would not help optimizing compilers
>
> It is not pointless because of the size of the function, but because `int`
> is already a type that is always passed by value, never by reference.

You are looking only at the prototype side (i.e. declaration in *.h). Yes it is pointless for the callers. For the callee, the story is different and pass-by-value does not even get in the picture.

The mention of pointless-ness I made was about the implementation side (i.e. definition in *.c). For a sufficiently large and complex function implementation, being able to say upfront that this incoming parameter is never modified would help following the logic in the implementation, so "const int param" in the parameter list of a definition is *not* pointless in general. But apparently some compilers are not happy abot "const int param" in implementation that is paired with "int param" in prototype, we are dropping a const that could be useful, with an excuse that for this particular function that is small and trivial, we can live without.