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Date: Tue, 1 Apr 2025 00:03:03 +0200
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To: PHP internals <internals@lists.php.net>
Subject: [PHP-DEV] [RFC brainstorm] Approximately equals operator
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From: dossche.niels@gmail.com (Niels Dossche)

Hi internals!

I'm excited to share what I've been working on!
I had an epiphany. I realized what we truly need to revolutionize PHP: a new operator.

Hear me out.
We live in an imperfect world, and we often approximate data, but neither `==` nor `===` are ideal comparison operators to deal with these kinds of data.

Introducing: the "approximately equal" (or "approx-equal") operator `~=` (to immitate the maths symbol ≃).
This combines the power of type coercion with approximating equality.
Who cares if things are actually equal, close enough amirite?

First of all, if `$a == $b` holds, then `$a ~= $b` obviously.
The true power lies where the data is not exactly the same, but "close enough"!

Here are some examples:

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.

Ever had trouble with users mistyping something? Say no more!
"This is a tpyo" ~= "This is a typo". It's typo-resistant!
However, if the strings are too different, then they're not approx-equal.
For example: "vanilla" ~= "strawberry" gives false.
How does this work?
* The strings are equal if their levenshtein ratio is <= 50%, so it's adaptive to the length.
* If the ratio is > 50%, then the shortest string comes first in the comparison, such that if we ever get a `~<` operator, then "vanilla" ~< "strawberry".

There is of course a PoC implementation available at: https://github.com/php/php-src/pull/18214
You can see more examples on GitHub in the tests, here is a copy:
```php
// Number compares
var_dump(2 ~= 1); // false
var_dump(1.4 ~= 1); // true
var_dump(-1.4 ~= -1); // true
var_dump(-1.5 ~= -1.8); // true
var_dump(random_int(1, 1) ~= 1.1); // true

// Array compares (just compares the lengths)
var_dump([1, 2, 3] ~= [2, 3, 4]); // true
var_dump([1, 2, 3] ~= [2, 3, 4, 5]); // false

// String / string compares
var_dump("This is a tpyo" ~= "This is a typo"); // true
var_dump("something" ~= "different"); // false
var_dump("Wtf bro" ~= "Wtf sis"); // true

// String / different type compares
var_dump(-1.5 ~= "-1.a"); // true
var_dump(-1.5 ~= "-1.aaaaaaa"); // false
var_dump(NULL ~= "blablabla"); // false
```

Note that this does not support all possible Opcache optimizations _yet_, nor does it support the JIT yet.
However, there are no real blockers to add support for that.

I look forward to hearing you!

Have a nice first day of the month ;)
Kind regards
Niels