Re: lambda coding style

[Hans-Peter Nilsson <hp@bitrange.com>]

On Wed, 10 Jan 2024, Jason Merrill via Gcc wrote:
> 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 [?

Also, what about trailing-type and mutable (above) when needing 
a line-break?

(FTR: in technical terms, trailing-type is known as the 
pointy-arrow-declaring-return-type thing :) the optional "-> 
type" between "(parms)" and "{ body }")

I suggest the obvious (to me): line up stuff after (params) with 
the opening brace for body, when needing a line-break before 
that item, and line-break *before* "->" .

brgds, H-P