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[130.44.146.16]) by smtp.gmail.com with ESMTPSA id w9-20020a05620a148900b0078322355fb7sm39491qkj.20.2024.01.10.18.34.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jan 2024 18:34:58 -0800 (PST) Message-ID: <230bc361-55a9-4bfb-9321-9ac8cbbdf0f6@redhat.com> Date: Wed, 10 Jan 2024 21:34:57 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: lambda coding style To: Marek Polacek Cc: GCC Mailing List References: <7b2c4b10-4134-4f1b-9597-de66d6072f16@redhat.com> <8ec9a379-0b69-4a3c-b105-57ff0e37464b@redhat.com> From: Jason Merrill In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,KAM_SHORT,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,RCVD_IN_SORBS_WEB,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 1/10/24 16:41, Marek Polacek wrote: > On Wed, Jan 10, 2024 at 04:24:42PM -0500, Jason Merrill 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 [? >> >> 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. > > Fair enough, I think that's better. > > I suppose we should add a note wrt lambdas to > https://gcc.gnu.org/codingconventions.html#Cxx_Conventions Indeed, that's my goal. Looking through the various lambdas already in the compiler, I see a good number already follow my suggested indentation, but a large majority omit the space between ] and (, so maybe we don't want it? Jason