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Date: Fri, 10 Mar 2023 21:04:26 +0200
Message-ID: <CAM0CcxhpMr_SstLCgcMfESTo4_H6yAPuBZb6B08KjbnKS97VfA@mail.gmail.com>
To: PHP Internals <internals@lists.php.net>
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Subject: First-class callable partial application
From: zsidelnik@gmail.com (Eugene Sidelnyk)

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Hello internals!
I'm just wondering why First class callable syntax doesn't allow partial
application?
Recently I stumbled across following scenario where it could be really
useful:

```
    public function __invoke(SendOtpCommand $command)
    {
        $this->cache->get($command->getPhone(), $this->storeOtp($command,
...));
    }

    private function storeOtp(SendOtpCommand $command, ItemInterface $item)
    {
        // some logic
    }
```

In this example, I supposed that the closure created will accept a single
parameter $item, and when it is called back, method storeOtp will accept
both $command and $item. As it turned out to be, it doesn't really work
this way.

Another simplified example:

```
// partial application
foo(bar(1, ...));

function foo(Closure $closure)
{
    $closure(2);
}

function bar(int $a, int $b)
{
    var_dump($a, $b); // 1, 2
}
```

Closure in foo accepts only one parameter. But when it is actually
dispatched, bar is called with two arguments.

Are there any pitfalls, which prevent implementation of this nifty feature?

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