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

From: Junio C Hamano <gitster@pobox.com>
Date: May 13, 2019, 23:24 UTC
Message-ID: <xmqqo9469buw.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <a6bfec76c85bbe9187b536ff78252b82e30e20d3.1557787395.git.gitgitgadget@gmail.com>

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com> writes:

Show 5 quoted lines

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> When this function was changed in a97d00799a19 (remote-curl: use
> post_rpc() for protocol v2 also, 2019-02-21) from file-local to global,
> the declaration was incorrectly missing the `const` qualifier.

I do not quite get it. Back when the function was file-scope static, it did not even have a separate declaration, and the definition the said commit added looks correct to me.

Having "const int size" parameter in the definition of a function does help the compilers and the developers by making sure any earlier reference to the parameter in the function would not modify it and cause later reference to obtain a different value.

But the parameter treated as a constant without getting modified during the invocation of the function is an implementation detail of the function; there is no point exposing that implementation detail to its callers. It does not even help the compilers handling the caller's compilation unit---the parameter is passed by value, so the caller knows that the callee would not modify it without "const" there.

Does the language even allow flagging "const int in the definition, int in the declaration" as a warning-worthy discrepancy?

> -void set_packet_header(char *buf, int size);
> +void set_packet_header(char *buf, const int size);