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Date: Tue, 04 Jan 2022 10:01:59 +0100
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Subject: Re: [PHP-DEV] [VOTE] User Defined Operator Overloads
From: come@chilliet.eu (=?ISO-8859-1?Q?C=F4me?= Chilliet)

Hello,

=46rom the RFC:

> If the left operand produces a TypeError due to the parameter types liste=
d in the implementation, the operation is not retried with the right operan=
d and the error is instead returned immediately. This is to help developers=
 encounter errors in their program logic as early as possible.

This feels wrong if I understand correctly.

Let=E2=80=99s say I create a class A and I want to add support for "2 / new=
 A()", which by default does not work.

I can do
class A
{
  operator /(int $other, OperandPosition $operandPos): mixed
 {
    return "example";
 }
}

Now someone wants to build on my work, and add a class B that supports "new=
 A() / new B()".

class B
{
  operator /(A $other, OperandPosition $operandPos): mixed
 {
    return "example";
 }
}

This will not work because it will first try A->{'/'}(B) that throws a Type=
Error? So it means what I was able to do for floats, cannot be done for my =
new classes afterwards? This is inconsistent I think. It also means it is n=
ot possible to extend any existing class with operators interacting with a =
new class, meaning you can only use operators among classes aware of each o=
ther, most likely from the same package/library.

Also, this was stated already I think but I did not see an answer, from RFC=
 example:
> class Matrix {
>     public function __construct(readonly public array $value) {}
> =20
>     public operator *(Matrix $other, OperandPosition $operandPos): Number
>     {
>         if ($operandPos =3D=3D OperandPosition::LeftSide) {
>             // Count of my columns needs to match
>             // count of $other rows
>         } else {
>             // Count of my rows needs to match
>             // count of $other columns
>         }
>     }
> }

The second branch of the if is dead code, as $matrix1 * $matrix2 will alway=
s call $matrix1->{'*'}($matrix2, LeftSide) and never the other way around.
This means that $operandPos is useless in all cases where operators are onl=
y typed againts the same type, and points to this design solution being wro=
ng.

There is =C2=ABWhy not interfaces?=C2=BB in the FAQ, does that mean that op=
erators cannot be added in interfaces? This is not stated clearly in the RF=
C.

Also, it is not clear if operator overload will affect comparison operation=
s used in core functions such as in_array, sort and so on.
Does implementing operator =3D=3D allows using in_array to find an object i=
n an array?
Which of these internal functions use =3D=3D and which use =3D=3D=3D, which=
 is not overloadable?
Does implementing operator <=3D> allows sorting of arrays containing my obj=
ects?

C=C3=B4me