Re: lambda coding style

[Jason Merrill <jason@redhat.com>]

On 1/10/24 15:59, Marek Polacek wrote:
> On Wed, Jan 10, 2024 at 02:58:03PM -0500, Jason Merrill via Gcc wrote:
>> What formatting style do we want for non-trivial lambdas in GCC sources?
>> I'm thinking the most consistent choice would be
>>
>> auto l = [&] (parms) // space between ] (
>>    {                  // brace on new line, indented two spaces
>>      return stuff;
>>    };
> 
> Sure, why not.  Consistency is what matters.  Thus far we seem
> to have been very inconsistent.  ;)
>   
>> By default, recent emacs lines up the { with the previous line, like an
>> in-class function definition; I talked it into the above indentation with
>>
>> (defun lambda-offset (elem)
>>    (if (assq 'inline-open c-syntactic-context) '+ 0))
>> (add-to-hook 'c++-mode-hook '(c-set-offset 'inlambda 'lambda-offset))
>>
>> I think we probably want the same formatting for lambdas in function
>> argument lists, e.g.
>>
>> algorithm ([] (parms)
>>    {
>>      return foo;
>>    });
> 
> And what about lambdas in conditions:
> 
> if (foo ()
>      && [&] (params) mutable
>         {
> 	 return 42;
>         } ())
> 
> should the { go just below [?

I think we don't want the { to go below the [ in general; that was the 
old emacs default behavior, and it produced lambda bodies with excessive 
indentation.

With my adjustment above, emacs indents the { two spaces from the &&, 
which seems a bit arbitrary but reasonable.

Jason