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Re: style convention: /*foo_p=*/ to annotate bool arguments

On 04/10/16 01:48, Martin Sebor wrote:
> In a recent review Jason and I discussed the style convention
> commonly followed in the C++ front end to annotate arguments
> in calls to functions taking bool parameters with a comment
> along the lines of
>   foo (1, 2, /*bar_p=*/true);
> I pointed out to Jason that in another code review, Jeff asked
> to remove the same comment from the middle-end [1].  In the
> interest of consistency Jason and I thought I should bring this
> up for discussion so we can all be clear on whether or not this
> is something worth standardizing and documenting.
> As a separate question, in the same discussion I mention to Jason
> a convention that I myself have found useful where the value of
> a default argument is indicated in a comment in a function
> definition that is declared elsewhere to take one, e.g., like so:
>   // In some header:
>   void foo (int, int, bool = -1);
>   // In some .c file:
>   void foo (int x, int y, bool bar_p /* = false */)
>   {
>     ...
>   }
> Jason thought this would be a good convention.  Is there any
> interest in/support for adopting it?

IMHO, a commenting convention that makes it easy to write incorrect and
misleading comments is far worse than a convention that omits the
comments entirely.

I am not involved in gcc development (I'm just an interested observer on
this list), so I don't know much about the coding style in gcc at the
moment.  But /I/ would prefer a style like this:

// In some header:
void foo(int x, int y, bool bar_p = true);

// In some .c file:
void foo(int x, int y, bool bar_p)

There are several differences, which gcc folks may or may not agree
with, but which might be worth considering:

1. "bool" should be either "true" or "false" - not an integer.

2. I think parameter names are important in declarations - they help
tell you what the function is, and how to use it.

(As an aside, I would /really/ like a gcc warning option that would
check for consistency in parameter names.  This would be particularly
useful if C++ ever gets a named parameter feature.)

3. In the implementation, there is /no/ comment about the default value
of "bar_p".  The implementation has to work correctly regardless of the
value of "bar_p", so knowing the default value is of little benefit.  If
it is relevant, perhaps because you want to emphasize a particular path
for speed, then a comment might be useful - but it is better to use code
(like __builtin_expect) than comments.  Comments make it easy to be
inconsistent, and are unnecessary when the same information is easily
available by looking at the header (modern IDE's make that quick).



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