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Bound-Erased Generic Types

55 yes

2 no

This RFC adds generic type syntax to PHP. Classes, interfaces, traits, functions, methods, closures, and arrow functions can declare type parameters; those parameters carry bounds, defaults, and variance markers; type arguments may be supplied at use sites and at call sites via turbofish.

final readonly class Pair<+L, +R> {
    public function __construct(
        public L $left,
        public R $right,
    ) {}
 
    public function swap(): Pair<R, L> {
        return new Pair($this->right, $this->left);
    }
}
 
final readonly class Box<+T> {
    public function __construct(
        public T $value,
    ) {}
 
    public function map<U>(callable $fn): Box<U> {
        return new Box(($fn)($this->value));
    }
 
    public function zip<O>(O $value): Box<Pair<T, O>> {
        return new Box(new Pair($this->value, $value));
    }
}
 
function identity<T>(T $value): T {
    return $value;
}
 
$greeting = new Box::<string>("hello, world");
$paired   = $greeting->zip::<int>(42);
$swapped  = $paired->value->swap();
$result   = identity::<Pair<int, string>>($swapped);

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96%

If you like it or not, generics are already used in the wild. Having a standardized syntax is, in my opinion, a no-brainer.

This RFC chooses its scope carefully, providing some safety where it is easy to do so, while delegating the rest to static analyzers and keeping backwards compatibility. With this, the different static analyzers can finally agree on certain behaviors, because they are part of the language.

Having the generic type information available through reflection opens up exciting new possibilities.

Keeping the doors open for future expansion is another very important win.

TL;DR: The RFC is very pragmatic given the design of PHP. Provides very solid foundation upon which to build that was missing and asked for a decade.