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Date: Wed, 18 Oct 2023 12:20:10 -0600
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Subject: Re: [PHP-DEV] Custom object equality
From: lanre@online-presence.ca (Lanre Waju)

I believe it's time to shift our focus away from backward compatibility 
(BC) concerns in major versions. In my opinion, genuine operator 
overloading is incomparable to the pseudo operator. I genuinely see the 
operator overloads as an invaluable addition to PHP 9

Lanre

On 2023-10-18 6:50 a.m., someniatko wrote:
> Hi internals,
>
> There is often a need to compare whether two objects are equal. For
> example, a popular [brick/money](https://packagist.org/packages/brick/money)
> library has a `Money` class, which has an `equals()` method. However, this
> becomes tedious to implement such methods, when multiple nested objects are
> involved. For instance, Money has an amount and a currency.
>
> There were already suggestions on the mailing list to allow "overloading"
> existing `==` operator, and some suggestions went even as far as
> overloading `<`, `>=` etc operators. However, overloading existing
> operators may lead to a BC break between the PHP version which does support
> the functionality, and which doesn't. It won't result in a BC break in case
> it's an entirely new syntax, because a library or a project won't be able
> to write code which overloads `==` in say PHP 8.4, but with code which
> still works in PHP 8.3 - it will have to require PHP 8.4+. But if it is
> implemented as a magic method, then `==` will work differently for 8.3 and
> 8.4.
>
> I suggest thinking about introducing a new operator `~=`, which signifies
> that custom equality is requested. In such a case,  `==` will work as it
> works now, and by default `~=` will work also like `==`, unless its
> behavior is overwritten via a magic method. If a magic method is not
> present in a class being compared, `~=` will compare two objects field by
> field, but using `~=` comparison rather than `==` comparison, recursively.
>
> For instance, a Money object may consist of Amount and Currency. If two
> Moneys are compared using `~=`, and Money does not implement a magic
> method, Amount also doesn't implement it, but Currency does, then Amounts
> are compared using  `~=` which is equal to `==` comparison in this case,
> but Currencies are compared using their custom comparison logic.
>
> This approach allows combining
> - no BC break - `~=` is a new syntax which is unavailable in older PHP
> versions
> - explicitly showing an intent that objects are compared using a custom
> comparison, rather than standard PHP one
> - allow to skip writing boilerplate equals() methods which just forward
> equals() to the nested objects
> - standardize such comparisons on the language level
>
> Of course how exactly this operator looks may be changed, `~=` is just an
> example.
>
> WDYT?
>
> Regards,
> Illia / someniatko
>