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Date: Tue, 26 Apr 2016 11:26:05 -0600
Message-ID: <CAFMT4NpKW6f5-N8Udb2obUF1PVvSXYsG+O0RDYsHwQS+U5tOPA@mail.gmail.com>
To: Niklas Keller <me@kelunik.com>
Cc: Bob Weinand <bobwei9@hotmail.com>, Dmitry Stogov <dmitry@zend.com>, 
	internals <internals@lists.php.net>, Joe Watkins <pthreads@pthreads.org>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] [RFC] Patch for Union and Intersection Types
From: morrison.levi@gmail.com (Levi Morrison)

On Tue, Apr 26, 2016 at 11:20 AM, Levi Morrison <morrison.levi@gmail.com> wrote:
> On Tue, Apr 26, 2016 at 11:00 AM, Niklas Keller <me@kelunik.com> wrote:
>> 2016-04-26 16:58 GMT+02:00 Bob Weinand <bobwei9@hotmail.com>:
>>>
>>> Yeah, I'd like to not allow ?Foo in any case if union types pass.
>>
>>
>> What's the reason for that? To me, null is neither a type nor should it be.
>
> On the contrary, our manual says:
>
>> NULL is the only possible value of type null.
>
> And internally it is also a distinct type.
>
> It's been this way for a long time; we just haven't permitted `null`
> as a type declaration because until now it has been useless.

To further expand on why it was previously useless:

    function foo(Null $a) {
        return $a;
    }

There is only one possibility for this parameter, which is the value
`NULL`. There is hardly any value to it when you can just write this
instead:

    function foo() {
        return NULL;
    }

In words: if the only possible value for a parameter is null then it's
not really a parameter; it's just a constant value and doesn't need to
be parameterized.