From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by sourceware.org (Postfix) with ESMTPS id 394C23858401 for ; Wed, 10 Aug 2022 16:03:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 394C23858401 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.cz Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 24EAE5C61E; Wed, 10 Aug 2022 16:03:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1660147431; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=P7OkAxShr5PrPqZNN7z2/HZ97xMo3nJAvigagz21Y9A=; b=wIOi+7gkZIITnGcooKYzTo49PPIoNaAw76oxwIAxvqe86s86N45HtE5YiaTKswZ3X3u9BM SiEWVdm7Pw6uqQHR/Mq2m4tcWyNtfVVr9tpRdqNeKb8O85zE6psTUS2C7Tk2TNccr3LdIO 5eOBHcRPnxGp2n9ZZbs4qFuzYg3b8L8= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1660147431; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=P7OkAxShr5PrPqZNN7z2/HZ97xMo3nJAvigagz21Y9A=; b=eMcz0vv7UzG1FBxqeR7jWWZufL0H7a3Vv19Awx6DqNSZoFFOgoZnOW2cUapedWv4FK+Wdv 1XadvHfgnesSdDCQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 0DC3D13AB3; Wed, 10 Aug 2022 16:03:51 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id SkmtAufW82KNYQAAMHmgww (envelope-from ); Wed, 10 Aug 2022 16:03:51 +0000 From: Martin Jambor To: Richard Sandiford , gcc-patches@gcc.gnu.org Subject: Re: [09/23] Add a cut-down version of std::span (array_slice) In-Reply-To: References: User-Agent: Notmuch/0.35 (https://notmuchmail.org) Emacs/28.1 (x86_64-suse-linux-gnu) Date: Wed, 10 Aug 2022 18:03:50 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-11.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, SPF_HELO_NONE, SPF_PASS, 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 X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Aug 2022 16:03:54 -0000 Hello, I have one more question/comment about array_slice. Ever since I started to use it... On Fri, Nov 13 2020, Richard Sandiford via Gcc-patches wrote: > A later patch wants to be able to pass around subarray views of an > existing array. The standard class to do that is std::span, but it's > a C++20 thing. This patch just adds a cut-down version of it. > > The intention is just to provide what's currently needed. > > gcc/ > * vec.h (array_slice): New class. > --- > gcc/vec.h | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 120 insertions(+) > > diff --git a/gcc/vec.h b/gcc/vec.h > index f02beddc975..7768de9f518 100644 > --- a/gcc/vec.h > +++ b/gcc/vec.h > @@ -2128,6 +2128,126 @@ release_vec_vec (vec > &vec) > vec.release (); > } > > +// Provide a subset of the std::span functionality. (We can't use std::span > +// itself because it's a C++20 feature.) > +// > +// In addition, provide an invalid value that is distinct from all valid > +// sequences (including the empty sequence). This can be used to return > +// failure without having to use std::optional. > +// > +// There is no operator bool because it would be ambiguous whether it is > +// testing for a valid value or an empty sequence. > +template > +class array_slice > +{ > + template friend class array_slice; > + > +public: > + using value_type = T; > + using iterator = T *; > + using const_iterator = const T *; > + > + array_slice () : m_base (nullptr), m_size (0) {} > + > + template > + array_slice (array_slice other) > + : m_base (other.m_base), m_size (other.m_size) {} > + > + array_slice (iterator base, unsigned int size) > + : m_base (base), m_size (size) {} > + > + template > + array_slice (T (&array)[N]) : m_base (array), m_size (N) {} > + > + template > + array_slice (const vec &v) > + : m_base (v.address ()), m_size (v.length ()) {} > + > + iterator begin () { return m_base; } > + iterator end () { return m_base + m_size; } > + > + const_iterator begin () const { return m_base; } > + const_iterator end () const { return m_base + m_size; } > + > + value_type &front (); > + value_type &back (); > + value_type &operator[] (unsigned int i); > + > + const value_type &front () const; > + const value_type &back () const; > + const value_type &operator[] (unsigned int i) const; > + > + size_t size () const { return m_size; } ...this has been a constant source of compile errors, because vectors have length () and this is size (). I understand that the motivation was consistency with std::span, but do we really want to add another inconsistency with ourselves? Given that array_slice is not that much used yet, I believe we can still change to be consistent with vectors. I personally think we should but at the very least, if we keep it as it is, I'd like us to do so deliberately. Thanks, Martin