From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Philipp Stephani Newsgroups: gmane.emacs.devel Subject: Re: [Emacs-diffs] master 74f54af: Use eassume (false) for branch that's never taken. Date: Fri, 19 Apr 2019 21:14:52 +0200 Message-ID: References: <83ftqecrms.fsf@gnu.org> <83ef5ycnny.fsf@gnu.org> <9b3a1717-64de-795a-2acf-0698576caf02@cs.ucla.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="82397"; mail-complaints-to="usenet@blaine.gmane.org" Cc: Philipp Stephani , Eli Zaretskii , Emacs developers To: Paul Eggert Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Apr 19 21:16:47 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1hHZ0B-000LJj-3v for ged-emacs-devel@m.gmane.org; Fri, 19 Apr 2019 21:16:47 +0200 Original-Received: from localhost ([127.0.0.1]:60317 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHZ0A-00087z-1s for ged-emacs-devel@m.gmane.org; Fri, 19 Apr 2019 15:16:46 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:58330) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHZ03-000873-Nx for emacs-devel@gnu.org; Fri, 19 Apr 2019 15:16:40 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hHYyX-0007TU-LZ for emacs-devel@gnu.org; Fri, 19 Apr 2019 15:15:06 -0400 Original-Received: from mail-ot1-x336.google.com ([2607:f8b0:4864:20::336]:38887) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1hHYyV-0007St-W0; Fri, 19 Apr 2019 15:15:04 -0400 Original-Received: by mail-ot1-x336.google.com with SMTP id e80so5057038ote.5; Fri, 19 Apr 2019 12:15:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=yLZXKlcOP+ZRjJWNroFslIrAIov7eVR244mRgs2yFjI=; b=jq16gQcjd0bNZX6eHpipUQGZLTJqwNT5qT245HE/Rknb6DM5RjsyENrhPNHDcz07LL q/f34lW6M4I21rcQ8vvH+Hai/NszpAfK/xzF04ruhGqGK9OixUv4qdrOWCCy4NVez1Do O6zKJ59mvqGFCTGJqQyxkUIb7kiS5zgkvCCpNIx0NdU3WwBnYRiepwuyEu/8yEfYOFZD mUJxtejvT3jarxVixwo/SWlt5iDyA+CAta5EUmSeQZWPlMOTfvKR+4Cm8B+QhjYr5/9S fMxL1+qY+wEXoS4LxJO8tQbFPGT7XMuDbgNzvgMG3nrgr6saybIVdJR+sd4X87icWgmA acVg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=yLZXKlcOP+ZRjJWNroFslIrAIov7eVR244mRgs2yFjI=; b=sXgGOcoKFUD3fYcPV2axokSm43YJpi1g8iofDaTaa2cR9cXdeXLz/X8N66AnUNXZKn rplAlxWuw30wPwc71jJMs4UQ6ice+O3FFeH8Fwosm+SgP/SLhOdRG88VzrHopHfCXpR+ 9N0icNmnSVk0j/PMsKf3bVVUqskIqoUDw/BIzjnibSmNqtzaLX4cFx/RFVQ6RTOvbvdl ZAmFxhrKm+LAS7vyTIbe8mY5bGYQerNsbKlX1lEJq64ROSvZyN++Hg8AxJkBDQ1OqYet q9b6kwORoHjjlPpw2LhNPoHqVw6sYgXnz+9GTZfH32TF+H40bIxLU6SU15/ytPqbTNQ2 XOjw== X-Gm-Message-State: APjAAAUSCnNo425NjqduvqEq1qHisVEj/FA570qaT0SII81OU0TygaNO elRBTL9DB7/4l49R/TNqscWDZS8rhzY0XCG6wDg= X-Google-Smtp-Source: APXvYqwvgukGSxX0Wdxhz55ztqBUP/ETWdzFcetmDrIgDNrLV08GtA2tj8Ry8TbY9KAHu625GPh0edZyyEq9eGutM20= X-Received: by 2002:a05:6830:15d2:: with SMTP id j18mr2985527otr.37.1555701303136; Fri, 19 Apr 2019 12:15:03 -0700 (PDT) In-Reply-To: <9b3a1717-64de-795a-2acf-0698576caf02@cs.ucla.edu> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::336 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:235668 Archived-At: Am Fr., 19. Apr. 2019 um 21:04 Uhr schrieb Paul Eggert : > > On 4/19/19 3:08 AM, Eli Zaretskii wrote: > > When ENABLE_CHECKING is not defined, which happens in every production > > build, eassume expands to code that has no side effects, so the > > function will return a random value to its caller. I don't think this > > is desired. > > It looks OK to me. The default branch is impossible, so the function > cannot return a random value to its caller. Although GCC is not smart > enough to deduce this fact, eassume lets the programmer communicate it > to GCC so that GCC doesn't issue a false-alarm diagnostic (and GCC also > can generate better code). When ENABLE_CHECKING is defined, there's also > a runtime check that the impossible does not happen, but this extra > check isn't needed in ordinary production. FWIW, I'm fine with both eassume(false) and emacs_abort. > > This would all be simpler if we replaced 'enum nonlocal_exit' with a > simple boolean. The enum seems to be more trouble than it's worth, if > it's causing this sort of bikeshedding. Not every boolean deserves an > enum just for it. > I tend to disagree: In APIs, booleans should only be used for values that have a clear false and true state (e.g. predicates). In other cases booleans reduce readability (because "false" and "true" are meaningless by themselves) and make extending unnecessarily hard. I'm actually surprised that compilers warn about the lack of the default case. The typical use for this construct is to signal that the switch statement intends to handle all cases, causing a compiler warning if new enumerators are added, which is very useful because it reminds you of the callers that need to be adapted. Therefore it's better to leave out the default case.