Re: [PHP-DEV] [Discussion] Revisiting typed closures

On 1 July 2026 20:02:27 BST, Seifeddine Gmati <[email protected]> wrote:
>Making `Closure` generic (e.g., say `Closure<Input, Output>` ) would
>require `Input` to be variadic to stand in for a closure's parameter
>list, and variadic generics are a different beast entirely.

FWIW, C# has a long list of overloads for expressing generic lambda types, like Action<T1,T2>, Action<T1,T2,T3>, Func<T1,T2,TResult> and so on and on and on <https://github.com/dotnet/dotnet/blob/b0f34d51fccc69fd334253924abd8d6853fad7aa/src/runtime/src/libraries/System.Private.CoreLib/src/System/Action.cs> <https://github.com/dotnet/dotnet/blob/b0f34d51fccc69fd334253924abd8d6853fad7aa/src/runtime/src/libraries/System.Private.CoreLib/src/System/Function.cs>

Ugly, and unlikely to even work in a PHP implementation of generics.

On the other hand, it has an elegant "delegate" syntax for what are effectively named callable types: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/

That *would* translate well to PHP. Translating one of their examples:

delegate ProcessBookCallback(Book $book): void;

public function processPaperbackBooks(ProcessBookCallback $processBook): void { 
    foreach ($this->list as $b) {
        if ($b->paperback) {
            $processBook($b);
        }
    }
}

Just an additional angle to throw into the mix.


Rowan Tommins
[IMSoP]