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Date: Tue, 01 Apr 2025 10:56:56 +0200
To: Niels Dossche <dossche.niels@gmail.com>
Cc: PHP internals <internals@lists.php.net>
Subject: Re: [PHP-DEV] [RFC brainstorm] Approximately equals operator
In-Reply-To: <4a3c6ce7-102d-4cfe-a7a8-35630715b870@gmail.com>
References: <4a3c6ce7-102d-4cfe-a7a8-35630715b870@gmail.com>
Message-ID: <ed95b17723d254abd514340501fcdb46@bastelstu.be>
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2025-04-01 00:03, schrieb Niels Dossche:
> We all had situations where we wanted to compare two floating point 
> numbers and it turns out that due to the non-exact representation, 
> seemingly-equal numbers don't match! Gone are those days because the 
> `~=` operator nicely rounds the numbers for you before comparing them.
> This also means that the "Fundamental Theorem of Engineering" now 
> holds!
> i.e. 2.7 ~= 3 and 3.14 ~= 3. Of course also 2.7 ~= 3.14. But this is 
> false obviously: 2 ~= 1.
> 

Thank you for your proposal. I've tried it and I believe I found some 
fundamental flaw in the current logic. Consider:

     <?php

     var_dump(1.499999 ~= 1.5);
     var_dump(1.399999 ~= 1.4);

This currently prints:

     bool(false)
     bool(true)

which violates my expectations. If 1.499999 is approximately equal to 
1.5 then 1.399999 should also be approximately equal to 1.4.

Best regards
Tim Düsterhus