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Subject: Re: [std-proposals] new approximately equal operators
From: Eyal Rozenberg (eyalroz_at_[hidden])
Date: 2020-06-08 18:04:11

What problem would adding this behavior solve? What is its significant

If it's merely the desire to write

   if (a ~= b)

instead of

   if (almost_equal(a, b))


   if (almost_equal<epsilon>(a, b))

(with almost_equal being a utility function you've implemented), then I
doubt the standard committee would find it worthwhile.

On 08/06/2020 22:52, Vishal Oza via Std-Proposals wrote:
> I was wondering if there is any interest in adding approximately equal
> to operators into the language. The main purpose is to compare floating
> point calculations with rounding error, however they could be used for
> similarity of objects or fixed point rounded values as well.
> the operator I propose are: ~=, ~< , ~>, ~!
> these operators would translate at least to floating point as
> a ~= b ==> abs(a-b) <  epsilon
> a ~< b ==> (a < b) || (abs(a-b) <  epsilon)
>  a ~> b ==> (a > b) || (abs(a-b) <  epsilon)
> a ~! b ==> abs(a-b) >=   epsilon
> There are two routes I can see with default implementation this language
> feature. either adding a default epsilon into the language that can be
> set as a global variable or adding some way of tracking errors. I would
> like more feedback on either way of default implementation.
> I would also like a way to specify the epsilon value or function for a
> single comparison. the best I can think of is
> a ~=b(c) ==>  abs(a-b) <  c
> a ~=b:c ==>  abs(a-b) <  c
> [c]a ~=b ==>  abs(a-b) <  c
> The precedence should be on the same level of all of the current
> comparison operators.
> This could be introduced in C++ 23 or later in there is any interate.
> Sincerely,
> Vishal Oza
> *This email is from an external mail server, be judicious when opening
> attachments or links *

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