Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle)

Subject	Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle)
Newsgroups	comp.lang.c++
References	<cYwKF.3051$vj3.487@fx10.dcg> <c7c7929d-b01c-4a19-a557-60da44ed6c9f@googlegroups.com>
From	Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk>
Organization	Jupiter Mining Corporation
Message-ID	<FpyKF.281$Rl7.139@fx06.dcg> (permalink)
Date	2019-12-18 23:14 +0000

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On 18/12/2019 22:24, Öö Tiib wrote:
> On Wednesday, 18 December 2019 23:35:23 UTC+2, Mr Flibble  wrote:
>> Hi!
>>
>> The following is the base class of my vector class (the mathematical vector not the container) so I can do things like:
>>
>> vec3 v1 = { 1.0, 2.0, 3.0 };
>> vec2 v2 = v1.xy;
>> double z = v1.z;
>> vec4 v3 = v1.xyzz;
>>
>> So we have an anonymous union of an anonymous struct and some swizzles and I suspect it is full of UB but I am finding it hard to care as I cannot see any other way of doing this.
>>
>> Collective thoughts/wisdom?
> 
> It likely violates strict aliasing, casting between unrelated types
> and also how unions are allowed to be used in C++.
> 
> So even if it appears to work with your compilers on cases
> you did test it might mess it up differently in other use-cases
> that you did not test yet. Also it may change with next patch to
> any of your compilers.
> 
> Can you say what is the issue with typical interface
> implementable to work same on all C++11 or better compilers:
> 
>   vec3 v1 = { 1.0, 2.0, 3.0 };
>   vec2 v2 = v1.xy();
>   double z = v1.z();
>   vec4 v3 = v1.xyzz();
> 
> Couple of extra parentheses can't be problem, otherwise we all
> would switch to Kotlin (that is *way* less verbose than C++).

Because

v1.set_z(42.0);

is ew and

v1.z() = 42.0

is even more ew.

/Flibble

-- 
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Thread

Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-18 21:34 +0000
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Öö Tiib <ootiib@hot.ee> - 2019-12-18 14:24 -0800
    Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-18 23:14 +0000
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Öö Tiib <ootiib@hot.ee> - 2019-12-18 15:36 -0800
        Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-19 06:18 +0000
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-12-19 10:49 +0100
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Manfred <noname@add.invalid> - 2019-12-19 14:29 +0100
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-12-18 15:38 -0800
    Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-19 06:19 +0000
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-12-23 10:34 -0800
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-12-28 00:30 -0800
        Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibble@i42.removethisbit.co.uk> - 2019-12-28 15:53 +0000
          Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-31 23:00 -0800
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Manfred <noname@add.invalid> - 2019-12-19 14:25 +0100
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) woodbrian77@gmail.com - 2019-12-20 08:22 -0800
    Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-12-21 13:23 +0000
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-11 15:08 -0800
    Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-10 18:35 +0100
      Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-02-10 14:07 -0800
  Re: Probably UB but I am finding it hard to give a fuck (C++ swizzle) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-31 21:42 -0800

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