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Date: Sat, 10 Sep 2016 20:01:44 +0200
Message-ID: <CADyq6sJjGGS30oVqjFvhYS96UpPwv4uhZBCTrZGdLm5K_HNbhQ@mail.gmail.com>
To: Niklas Keller <me@kelunik.com>
Cc: =?UTF-8?Q?Silvio_Mariji=C4=87?= <marijic.silvio@gmail.com>, 
	PHP Internals List <internals@lists.php.net>, Larry Garfield <larry@garfieldtech.com>
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Subject: Re: [PHP-DEV] RFC - Immutable classes
From: ocramius@gmail.com (Marco Pivetta)

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On Sat, Sep 10, 2016 at 7:49 PM, Niklas Keller <me@kelunik.com> wrote:

> 2016-09-10 19:41 GMT+02:00 Silvio Mariji=C4=87 <marijic.silvio@gmail.com>=
:
>
> > @Fleshgrinder,
> >
> > While I'm not sure at the moment about CoW, I can agree that we should
> add
> > immutable keyword as a interface modifier to make sure all classes
> > implementing must be immutable.
>
>
> As interfaces can't have member variables, that doesn't make sense to me.
>

It still makes sense from a consumer perspective, so having the restriction
in the contract is quite good.

If you accept a `Number`, you expect to be able to serialize/de-serialize
it, and you expect it to be "locked", immutable.
If you let an implementation of `Number` to have mutable state in, then you
break all the code that relies on `Number`.
Note that it is still possible to break this though, so maybe we'd need
some other modifiers about behavior too (pure function modifier?)

immutable interface Number
{
    public function toFloat() : float;
}
immutable class RandomNumber implements Number
{
    public function toFloat() : float { return (float) random_int(1,
100000); /* yo, look at my global mutable hidden state! */ }
}

Requiring immutable values in consumers will likely improve code
quality/safety and reduce dangerous assumptions, and it will probably also
allow for optimizations in the engine later on.

Marco Pivetta

http://twitter.com/Ocramius

http://ocramius.github.com/

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