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Subject: Re: [std-proposals] Prevent Assignments from contextually converting to bool
From: Tjernstrom, Staffan (Staffan.Tjernstrom_at_[hidden])
Date: 2019-10-23 12:11:30


" Code that intends to do this can simply put parenthesis around the assignment or use an init-statement,"

This would break compatibility with a lot of existing code, especially of the C-compatible forms

if ( num_read = read( buff, count, 1, fd ) )
{
   handle_buffer( buff, num_read );
}

-----Original Message-----
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Sent: Wednesday, 23 October, 2019 13:00
To: std-proposals_at_[hidden]
Subject: Std-Proposals Digest, Vol 7, Issue 40

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Today's Topics:

   1. Re: Reply to Herb Sutter about Zero-Overhead deterministic.
      It is not true. (Ville Voutilainen)
   2. Re: Reply to Herb Sutter about Zero-Overhead deterministic.
      It is not true. (Arthur O'Dwyer)
   3. Re: Reply to Herb Sutter about Zero-Overhead deterministic.
      It is not true. (Ville Voutilainen)
   4. Prevent Assignments from contextually converting to bool
      (connor horman)
   5. Re: Prevent Assignments from contextually converting to bool
      (Brian Bi)

----------------------------------------------------------------------

Message: 1
Date: Wed, 23 Oct 2019 17:50:24 +0300
From: Ville Voutilainen <ville.voutilainen_at_[hidden]>
To: sotrdg sotrdg via Std-Proposals <std-proposals_at_[hidden]>
Cc: "Arthur O'Dwyer" <arthur.j.odwyer_at_[hidden]>, sotrdg sotrdg
<euloanty_at_[hidden]>
Subject: Re: [std-proposals] Reply to Herb Sutter about Zero-Overhead
deterministic. It is not true.
Message-ID:
<CAFk2RUaLrzgVkbmV2T2j8RCrU_7jeLP-jBbrKO3PQPFFK9f+kA_at_[hidden]>
Content-Type: text/plain; charset="UTF-8"

On Wed, 23 Oct 2019 at 17:38, Arthur O'Dwyer via Std-Proposals <std-proposals_at_[hidden]> wrote:
> (Furthermore, I think that C++2a [and C++2b] should be delayed.)

That record you're playing is broken.

------------------------------

Message: 2
Date: Wed, 23 Oct 2019 12:04:01 -0400
From: "Arthur O'Dwyer" <arthur.j.odwyer_at_[hidden]>
To: Ville Voutilainen <ville.voutilainen_at_[hidden]>
Cc: sotrdg sotrdg via Std-Proposals <std-proposals_at_[hidden]>
Subject: Re: [std-proposals] Reply to Herb Sutter about Zero-Overhead
deterministic. It is not true.
Message-ID:
<CADvuK0Jgi39sU+Rfwf8v1mZpRPgT0w_je95EpRcb4_L=SzyCiQ_at_[hidden]>
Content-Type: text/plain; charset="utf-8"

On Wed, Oct 23, 2019 at 10:50 AM Ville Voutilainen < ville.voutilainen_at_[hidden]> wrote:

> On Wed, 23 Oct 2019 at 17:38, Arthur O'Dwyer via Std-Proposals
> <std-proposals_at_[hidden]> wrote:
> > (Furthermore, I think that C++2a [and C++2b] should be delayed.)
>
> That record you're playing is broken.
>

Not as broken as C++2a. ;)

?Arthur
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Message: 3
Date: Wed, 23 Oct 2019 19:13:41 +0300
From: Ville Voutilainen <ville.voutilainen_at_[hidden]>
To: "Arthur O'Dwyer" <arthur.j.odwyer_at_[hidden]>
Cc: sotrdg sotrdg via Std-Proposals <std-proposals_at_[hidden]>
Subject: Re: [std-proposals] Reply to Herb Sutter about Zero-Overhead
deterministic. It is not true.
Message-ID:
<CAFk2RUbS22twr_2bx9uvDZ1va3xjXWvtBTEzmL_E76oNDRcYvg_at_[hidden]>
Content-Type: text/plain; charset="UTF-8"

On Wed, 23 Oct 2019 at 19:04, Arthur O'Dwyer <arthur.j.odwyer_at_[hidden]> wrote:
>
> On Wed, Oct 23, 2019 at 10:50 AM Ville Voutilainen <ville.voutilainen_at_[hidden]> wrote:
>>
>> On Wed, 23 Oct 2019 at 17:38, Arthur O'Dwyer via Std-Proposals
>> <std-proposals_at_[hidden]> wrote:
>> > (Furthermore, I think that C++2a [and C++2b] should be delayed.)
>>
>> That record you're playing is broken.
>
>
> Not as broken as C++2a. ;)

That's almost as funny as other kinds of trolls on the internet, i.e. not very.

------------------------------

Message: 4
Date: Wed, 23 Oct 2019 12:35:18 -0400
From: connor horman <chorman64_at_[hidden]>
To: std-proposals_at_[hidden]
Subject: [std-proposals] Prevent Assignments from contextually
converting to bool
Message-ID:
<CADLV35iaJ98ym2Xs-qXncsNFws1Ek4FH8NhKq9ToetuMKiy88g_at_[hidden]>
Content-Type: text/plain; charset="utf-8"

This is my proposed to solution to one of the worst logic errors in any number of languages, being:
if(i=0)
vs.
if(i==0)

The proposal is to tweak the wording of contextual conversions to bool, prohibiting unparenthesised assignments from being eligible for contextual conversion. Code that intends to do this can simply put parenthesis around the assignment or use an init-statement, and code that does this without intention (i.e. intends the comparison) would be elevated from a logic error (the worst kind honestly) to a compile-time error.
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Message: 5
Date: Wed, 23 Oct 2019 11:43:45 -0500
From: Brian Bi <bbi5291_at_[hidden]>
To: std-proposals_at_[hidden]
Subject: Re: [std-proposals] Prevent Assignments from contextually
converting to bool
Message-ID:
<CAMmfjbOsk0K40UDzmermppiDCatDrePeQd1LCbisiOEfWyXC1A_at_[hidden]>
Content-Type: text/plain; charset="utf-8"

On Wed, Oct 23, 2019 at 11:35 AM connor horman via Std-Proposals < std-proposals_at_[hidden]> wrote:

> This is my proposed to solution to one of the worst logic errors in
> any number of languages, being:
> if(i=0)
> vs.
> if(i==0)
>
> The proposal is to tweak the wording of contextual conversions to
> bool, prohibiting unparenthesised assignments from being eligible for
> contextual conversion. Code that intends to do this can simply put
> parenthesis around the assignment or use an init-statement, and code
> that does this without intention (i.e. intends the comparison) would
> be elevated from a logic error (the worst kind honestly) to a compile-time error.
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>

You can achieve this effect using compiler warnings. For example, with GCC and Clang, you can use the flag -Werror=parentheses to treat this as an error.

I do not think we should add more rules to the language that discriminate among expressions on the basis of properties other than their type and value category.

--
*Brian Bi*
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