From nobody Wed Dec 1 16:02:54 2021 Return-Path: X-Original-To: cbor@ietfa.amsl.com Delivered-To: cbor@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id A13093A0D17 for ; Wed, 1 Dec 2021 16:02:52 -0800 (PST) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -2.097 X-Spam-Level: X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EQ5u-MB2qd5t for ; Wed, 1 Dec 2021 16:02:47 -0800 (PST) Received: from mail-yb1-xb2f.google.com (mail-yb1-xb2f.google.com [IPv6:2607:f8b0:4864:20::b2f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 3B7C43A0D09 for ; Wed, 1 Dec 2021 16:02:47 -0800 (PST) Received: by mail-yb1-xb2f.google.com with SMTP id q74so68309470ybq.11 for ; Wed, 01 Dec 2021 16:02:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=MgTPq0czc5m0UnDwq+hi//LTC2Tf6uYq8lKsTVvVVTw=; b=AcYMZa2ihzLWgJISRXBh8FiTSFZfy9/B5HUMwBLvtMNcva/RiEmUVWlaRoluKfpyH0 bMbvtAbHDbud+mnV6PcbuOLRw0RZIaProa1f4AVhMUVZ1yLcrtoK/xmh1FHtx+129yE+ khEo9cYsMFiGukwBf/aIYouRyxYUiawzP6TZ+zrEqy+jrPG5owgL6Jz/6efYwVGS36xk HEo3hhtgs1j0iTbWpNiQst6TSbvfM6cxmfmFIgmoyRwrsN0VEpMZ0YIUmAOQ8v/PXFck rq4nhsIejgDWXQmLfl6hKwYDIoPKl7XCw1/9lCG8TV/+AkAWxuBXsbC4zcmb/RCCH15m nhrg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=MgTPq0czc5m0UnDwq+hi//LTC2Tf6uYq8lKsTVvVVTw=; b=wgeJOl7L8wO0iHxGro9I2n3JnPU8PlglqERQf3J2l0fgWLHGXXv5xr5J7EQjaPR6Xd 1bAYw5OCpKtAiIAZnvxiCO9T+D3cCOiDeKxDWMzBJBJWX502/St4g1gI3++l4s7gCzxT eWG1dqsaHuwTdDKxJf6yjbIu7ud1kWWWQVu3ndiFbsEAA3JyHZmctg69Ks3FD+hU9A7q pGwo7tFGZOgehj7pXgbrQE22ZGd3W/T7qiIaE5YUqSRr366c0RNPufstg+qWySRoS5ek BXkbxtQ6AS5BLNS1hZijTtFf3RZHDtsr6cckdBI2ojRET0eQmMFgJf9oPZ0o1frarCpv 6AqQ== X-Gm-Message-State: AOAM533YzrPq6izRr2J1db89OZk4Fy+T+Uifa22xahUlsl2tUB1fCQ9o eb2X9eVCuPEvpm+Ib1L/+xlm7vZkfmoSCDO1uoo= X-Google-Smtp-Source: ABdhPJyil1w7Gsc/q7xl/MIDibV0ANeISJT9xn99oUDx5JYXAJ3XiGozbaXZ1dwfkhrdW33ZDSsrtDqGZSVd4Rvi60g= X-Received: by 2002:a25:bfca:: with SMTP id q10mr10689134ybm.68.1638403365049; Wed, 01 Dec 2021 16:02:45 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Emile Cormier Date: Wed, 1 Dec 2021 20:02:34 -0400 Message-ID: To: Carsten Bormann , cbor@ietf.org Content-Type: multipart/alternative; boundary="0000000000009299d405d21e82e3" Archived-At: Subject: Re: [Cbor] CBOR tag proposal for enumerated alternatives (tagged unions) X-BeenThere: cbor@ietf.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Concise Binary Object Representation \(CBOR\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Dec 2021 00:02:53 -0000 --0000000000009299d405d21e82e3 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable I don't know where we are with this proposal, but I'd like to point that it suffers from the same problem I've mentioned recently for bignum and records: too much information is embedded in the tag, which results in the data items being unusable when transcoded to JSON (or when a CBOR decoder discards the tags). Cheers, Emile Cormier On Wed, Apr 7, 2021 at 6:37 PM Emile Cormier wrote: > On Wed, Mar 31, 2021 at 9:38 AM Carsten Bormann wrote: > >> I=E2=80=99m not sure we discussed this one yet in detail: >> >> >> https://docs.google.com/document/d/16aiDEBhJj3kipj_7PVppEhxAr5E6QhQreN61= eCxvBjU/edit# >> >> This is a (cbor-tags) registration request, so the WG does not have to >> have an opinion, but the designated expert would be interested in it >> nonetheless. >> (I=E2=80=99m personally pretty convinced of the use case; this is more o= f an >> issue of keeping tabs on available tag numbers and looking out for relat= ed >> use cases.) >> > > As I had mentioned in the interim meeting, a related use case is > optional (aka Nullable). The meeting host (Christian?) was > questioning whether separate tags would be more appropriate to represent > the optional semantic. > > It would indeed be possible for the enumerated alternatives tags to be > used for representing an optional. For instance, alternative 0 would > represent the "no value" state, followed by a null data item (0xF6), > whereas alternative 1 would represent the "has value" state followed by t= he > actual value. However, this is just an arbitrary convention and the > enumerated alternatives tags used in this fashion don't explicitly expres= s > the "optional" semantic (it has to be assumed by the application). I > therefore agree that separate tags would be preferable for the optional > use case. > > I communicated with one of the co-authors of the enumerated alternatives > proposal about the possibility of including extra tags for the optional > use case. They declined, not wanting to expand the scope of their proposa= l, > which is perfectly understandable. > > My idea of tags for representing optional might be overkill. One can > simply encode an optional value as either null (0xF6) or the actual value= . > A contrived example where this would not work is encoding > optional (i.e. "optional null"). > > Anyway, the idea of tags for optional values is out there for the > designated expert to consider. I cannot say if it's an idea actually wort= h > pursuing. I don't currently need them for encoding/decoding > std::optional in my C++ work (I just check for null when deserializing > an optional value). However, I could definitely make use of the enumerate= d > alternatives tags for encoding/decoding std::variant, > especially when the alternative types are ambiguous once converted to CBO= R. > > Cheers, > Emile Cormier > --0000000000009299d405d21e82e3 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
I don't know where we are with this proposal, but= I'd like to point that it suffers from the same problem I've menti= oned recently for bignum and records: too much information is embedded in t= he tag, which results in the data items being unusable when transcoded to J= SON (or when a CBOR decoder discards the tags).

Ch= eers,
Emile Cormier

On Wed, Apr 7, 2021 at 6:37 PM Emile= Cormier <emile.cormier.jr= @gmail.com> wrote:
On Wed, Mar 31, 2021 at 9:38 AM Carsten Bormann <cabo@tzi.org> wrote:
I=E2=80=99m not su= re we discussed this one yet in detail:

https://docs.go= ogle.com/document/d/16aiDEBhJj3kipj_7PVppEhxAr5E6QhQreN61eCxvBjU/edit#<= br>
This is a (cbor-tags) registration request, so the WG does not have to have= an opinion, but the designated expert would be interested in it nonetheles= s.
(I=E2=80=99m personally pretty convinced of the use case; this is more of a= n issue of keeping tabs on available tag numbers and looking out for relate= d use cases.)

As I had mentioned in the= interim meeting, a related use case is optional<T> (aka Nullable<= T>). The meeting host (Christian?) was questioning whether separate tags= would be more appropriate to represent the optional<T> semantic.

It would indeed be possible for the enumerated altern= atives tags to be used for representing an optional<T>. For instance,= alternative 0 would represent the "no value" state, followed by = a null data item (0xF6), whereas alternative 1 would represent the "ha= s value" state followed by the actual value. However, this is just an = arbitrary convention and the enumerated alternatives tags used in this fash= ion don't explicitly express the "optional" semantic (it has = to be assumed by the application). I therefore agree that separate tags wou= ld be preferable for the optional<T> use case.

I communicated with one of the co-authors of the enumerated alternat= ives proposal about the possibility of including extra tags for the optiona= l<T> use case. They declined, not wanting to expand the scope of thei= r proposal, which is perfectly understandable.

My = idea of tags for representing optional<T> might be overkill. One can = simply encode an optional value as either null (0xF6) or the actual value. = A contrived example where this would not work is encoding optional<null_= type> (i.e. "optional null").

Any= way, the idea of tags for optional values is out there for the designated e= xpert to consider. I cannot say if it's an idea actually worth pursuing= . I don't currently need them for encoding/decoding std::optional<T&= gt; in my C++ work (I just check for null when deserializing an optional va= lue). However, I could definitely make use of the enumerated alternatives t= ags for encoding/decoding std::variant<T0, T1, T2...>, especially whe= n the alternative types are ambiguous once converted to CBOR.

Cheers,
Emile Cormier
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