Re: [RFC] Data Classes

On 23/11/2024 20:27, Rob Landers wrote:

Interesting! I actually found it to be intuitive. Think of it like this: function increment(array $array) {   $array[0]++; } $arr = [0]; increment($arr); echo $arr[0]; // is 0 We don't expect $arr to be any different outside of the function because $arr is a value, not a reference.

My mental model, rightly or wrongly, is that passing to a parameter is a bit like an assignment to a local variable: function increment(array) {    $array = $__args[0];    $array[0]++; } (This is explicitly how subroutine parameters work in Perl; I don't know if that's affected my mental model, or just means Larry Wall pictured it the same way.) You can even assign a new value to it, like any other variable: function whatever(array $array) {    $array = 'not even an array any more'; } But in PHP, $this isn't a parameter, and it's never possible to assign a new value to $this; so it feels completely alien to have a method where $this stops referring to the current object, and becomes a local variable.

I think it would be clearer to prevent direct modification of $this:

Not that I disagree (see the records RFC), but at that point, why not make data classes implicitly readonly?

I'm only suggesting restricting mutation on $this, not on the object itself. $foo->x++ would still work, and have automatic copy-on-write; but $this->x++ would be an error on a data class, just as $this=$bar is an error on all existing objects.

That would still be compatible with Ilija's suggestion, which was to add special "mutating methods":

I actually find this appealing, but it is strange to me to allow this syntax on classes. Is there precedent for that? Or is there a way we can do it using "regular looking PHP"; or are structs the way to go?

The way I see it, it's just a third type of method, to add to the two we already have: - instance methods: $this refers to the current instance - static methods: $this is forbidden - mutating methods: $this refers to the desired result of the mutation In fact, it's a bit like __construct or __clone, where $this refers to the newly created/copied object, before anything else points to it. -- Rowan Tommins [IMSoP]