adds isStatic and isNotStatic

[peterfox]

Changes

• Adds the assertions isStatic and isNotStatic.
• Adds tests.
• Updates the readme docs.

Why

This can be useful in some libraries where you want to make sure that the end user hasn't provided a static function as an argument.

Assert::isStatic($closure, $message = '');
Assert::isNotStatic($closure, $message = '');

[zerkms]

you want to make sure that the end user hasn't provided a static function as an argument.

what would be a real life use case for this exactly? What property of a static function can break 3rd party code versus non-static function that simply does not use $this?

[peterfox]

So if you're writing an API that accepts a Closure but contextually binds it later on it will stop the code from working.

$obj = new stdClass();
$function = static function () {
    return 'foo';
};
$function->bindTo($obj);

This would then throw an exception like 'Cannot bind an instance to a static closure'.

A good example of where I've seen this happen is with Pest where you provide closures where the Closure is then bound to a different object.

There's probably less of a need for isStatic than there is isNotStatic.

[shadowhand]

This is not type safe, because:

• The argument $closure is not typed, except with a docblock
• The docblock says Closure, but is enforced with isCallable
• The assertion isCallable uses is_callable(), which has type callable|mixed
• But ReflectionFunction accepts Closure|string

End result, the input type is enforced as callable and then passed to a constructor that accepts Closure|string. I believe the correct solution here is to type cast:

```php
if (($closure instanceof Closure) === false) {
    $closure = Closure::fromCallable($closure);
}

[peterfox]

Fixed by just type hinting as that made the most sense to me. It also then matches the throws assertion.