Re: [Discussion] Revisiting typed closures

> I would rather wait for generics and possibly make Closure a generic type. Fair point, but I am worried that's misleading, and I would keep the two separate. Generics are a much larger and more contentious topic; typed closure is a much smaller topic: a runtime shape check on a Closure value at the boundary, nothing more. The concrete benefit is typing the callback a higher-order method takes, so a mismatched map/filter callback is caught at the call site rather than deep inside the operation (or only by static analysis): ```php // expected signature: (int) => bool public function filter(Closure(int): bool $pred): static; // ok $nums->filter(fn(int $n): bool => $n % 2 === 0); // TypeError: string not expected $nums->filter(fn(string $s): bool => $s !== ''); ``` Typed closures neither need generics nor blocks them. In fact, eventually typed closures will support generics. But I would rather keep these topics separate. On its own, is a runtime-checked closure signature something you would find useful?