220 2273 <2c2b9360-8e5e-422d-9b85-124bd947b004@isocpp.org> article Path: news.gmane.org!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: optional, one more value or two states Date: Fri, 25 Jan 2013 12:20:36 -0800 (PST) Lines: 133 Approved: news@gmane.org Message-ID: <2c2b9360-8e5e-422d-9b85-124bd947b004@isocpp.org> References:

Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_144_19398978.1359145236245" X-Trace: ger.gmane.org 1359145238 26067 80.91.229.3 (25 Jan 2013 20:20:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 25 Jan 2013 20:20:38 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCEKFTV6ZUMBBFOSROEAKGQEBRY5PJA@isocpp.org Fri Jan 25 21:20:58 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ia0-f198.google.com ([209.85.210.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Typlg-0004VL-3D for gclcip-std-proposals@m.gmane.org; Fri, 25 Jan 2013 21:20:56 +0100 Original-Received: by mail-ia0-f198.google.com with SMTP id h23sf1656995iae.9 for ; Fri, 25 Jan 2013 12:20:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:date:from:to:message-id :in-reply-to:references:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-google-group-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=HSfU3d+bjIu7Uj8+t7/PTh6OlUHn8Vj1rCx1VN2dSQ8=; b=UHWLWYD6KVcytSm6+HG15ie1PGR0WY2vxxmfPXR54E80dafAQ6YXkFM/di5c+sIulT Bkj5JlMRnB3VAjyk4mUj2O+OmFLxZQEkMmrXs62RxUQjnWjsB+ZH1sQQOe3QY3pNyNST uymYSnUkTqZHR3CJvYx4m2sVytoWUH2fNvlUo1jnsxflLT7nyW/2I7YZR/MP8LL/V2rx Oq3QTEzvSFj5oZqloY6+adAEe/+j/YH2f/Q6qOEqPPftrP9QxezQzSsTe6BZ7zFhTMOH 5Dl6YYJ8ImCcNUnYVZdVus/rQqt13YfBdEHMUfzXAb8JE7I/a8ZchYtlQ3BROWKIPYY0 FjCw== X-Received: by 10.42.39.1 with SMTP id f1mr4874262ice.4.1359145238018; Fri, 25 Jan 2013 12:20:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.197.168 with SMTP id iv8ls642974igc.34.gmail; Fri, 25 Jan 2013 12:20:37 -0800 (PST) X-Received: by 10.50.5.174 with SMTP id t14mr2291809igt.11.1359145237359; Fri, 25 Jan 2013 12:20:37 -0800 (PST) In-Reply-To: X-Original-Sender: jmckesson@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:2273 Archived-At: ------=_Part_144_19398978.1359145236245 Content-Type: text/plain; charset=ISO-8859-1 On Friday, January 25, 2013 8:05:06 AM UTC-8, Tony V E wrote: > > On Fri, Jan 25, 2013 at 1:55 AM, Nicol Bolas > > wrote: > > > > > > On Thursday, January 24, 2013 8:56:08 PM UTC-8, Tony V E wrote: > >> > >> On Thu, Jan 24, 2013 at 7:10 PM, Dean Michael Berris > > >> wrote: > >> > > >> > In my opinion: > >> > > >> > - There's a precedent in other languages for a ".get(default_value)". > >> > Why don't we have this for optional instead? > >> > > >> > >> opt.get(17) doesn't look like it is using a default to me. Typically > >> get(17) is get the 17th element or lookup with key = 17, etc. > >> > >> > >> > - Why are we forcing pointer semantics on optional? Maybe there's a > >> > different concept here at play. > >> > > >> > >> Because much of optional's interface is similar to pointers: you > >> access the value with *opt and opt can be NULL. > >> > >> That is the essential "problem" with optional. Sometimes it acts > >> value-ish, sometimes pointer-ish. It is like quantum physics - > >> sometimes a particle, sometimes a wave... > > > > > > But it doesn't act like a pointer. Indeed, the *only* thing > "pointer-ish" > > about it is that it has an `operator*`. In every other way, it acts like > a > > value. > > And can be NULL. > No, it can be *empty*, not NULL. `optional` is a container. -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To post to this group, send email to std-proposals@isocpp.org. To unsubscribe from this group, send email to std-proposals+unsubscribe@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/?hl=en. ------=_Part_144_19398978.1359145236245 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

On Friday, January 25, 2013 8:05:06 AM UTC-8, Tony V E wrote:On Fri, Jan 25, 2013 at 1:55 AM, Nic= ol Bolas <jmck...@gmail.com> wrote:
>
>
> On Thursday, January 24, 2013 8:56:08 PM UTC-8, Tony V E wrote:
>>
>> On Thu, Jan 24, 2013 at 7:10 PM, Dean Michael Berris <db= e...@google.com>
>> wrote:
>> >
>> > In my opinion:
>> >
>> > - There's a precedent in other languages for a ".get(defa= ult_value)".
>> > Why don't we have this for optional instead?
>> >
>>
>> opt.get(17) doesn't look like it is using a default to me. &nb= sp;Typically
>> get(17) is get the 17th element or lookup with key =3D 17, etc= ..
>>
>>
>> > - Why are we forcing pointer semantics on optional? Maybe= there's a
>> > different concept here at play.
>> >
>>
>> Because much of optional's interface is similar to pointers: &= nbsp;you
>> access the value with *opt and opt can be NULL.
>>
>> That is the essential "problem" with optional. Sometimes= it acts
>> value-ish, sometimes pointer-ish. It is like quantum phy= sics -
>> sometimes a particle, sometimes a wave...
>
>
> But it doesn't act like a pointer. Indeed, the *only* thing "point= er-ish"
> about it is that it has an `operator*`. In every other way, it act= s like a
> value.

And can be NULL.

No, it can be empty, n= ot NULL. `optional` is a container.

--

---
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