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Date: Fri, 30 Jan 2015 18:39:32 +0300
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To: PHP internals list <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Immutable variables and objects
From: lisachenko.it@gmail.com (Alexander Lisachenko)

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2015-01-30 18:07 GMT+03:00 Andrea Faulds <ajf@ajf.me>:

> This approach wouldn=E2=80=99t solve the problem you=E2=80=99re describin=
g. You *still*
> need to produce a new request object, because the request object is
> immutable. The mutability of its *properties* isn=E2=80=99t the issue.



Thank you for this answer. However, pay an attention to the last part of my
suggestion. To create a mutable copy of immutable object it will be
possible just to make an assignment (this will create a copy/clone) to a
local mutable variable and adjust it for your needs.

example:

public function handleRequest(const Request $request) { // Mark $request as
immutable for body
    // we can not change $request variable itself
    // but if need, we can only initialize a copy of it
    // $request->url =3D 'https://evil.com'; // Exception will be there

    $mutableSubRequest =3D $request; // copy of immutable object or maybe a
direct Copy-on-Write?
    $mutableSubRequest->uri =3D 'https://example.com'; // It's ok to modify
our local copy of an object
    $this->kernel->handleRequest($mutableSubRequest);
}

2015-01-30 18:07 GMT+03:00 Andrea Faulds <ajf@ajf.me>:

> Hi Alexander,
>
> > On 30 Jan 2015, at 13:07, Alexander Lisachenko <lisachenko.it@gmail.com=
>
> wrote:
> >
> > Hello, internals!
> >
> > Today I was looking at PSR-7 and discovered this part of code:
> >
> > $body =3D new StringStream(json_encode(['tasks' =3D> [
> >    'Code',
> >    'Coffee',
> > ]]));;
> > $request =3D $baseRequest
> >    ->withUri($uri->withPath('/tasks/user/' . $userId))
> >    ->withMethod('POST')
> >    ->withHeader('Content-Type' =3D> 'application/json')
> >    ->withBody($body);
> > $response =3D $client->send($request);
> >
> > What is wrong here? Emulated immutability. All methods will create a
> > separate instance of request, so
> > $baseRequest->withUri()->withMethod()->withHeader()->withBody() will
> create
> > total 5 object instances. It's a memory overhead and time consumption f=
or
> > each method call.
>
> Yes, I also think this is unfortunate.
>
> > What I want to discuss is true immutability flag for variables and
> > parameters. There are a lot of languages that use "final" or "const"
> > keywords to prevent modification of variables. We can use this approach
> by
> > extending language syntax as following:
>
> This approach wouldn=E2=80=99t solve the problem you=E2=80=99re describin=
g. You *still*
> need to produce a new request object, because the request object is
> immutable. The mutability of its *properties* isn=E2=80=99t the issue.
>
> If you want to avoid creating five different objects, you=E2=80=99d need =
to
> implement value-type objects that are passed by value and use
> copy-on-write. Basically, you=E2=80=99d need to re-add PHP 4 style classe=
s.
>
> Thanks.
> --
> Andrea Faulds
> http://ajf.me/
>
>
>
>
>

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