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Date: Fri, 30 Jan 2015 15:07:28 +0000
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To: Alexander Lisachenko <lisachenko.it@gmail.com>
Subject: Re: [PHP-DEV] [RFC] Immutable variables and objects
From: ajf@ajf.me (Andrea Faulds)

Hi Alexander,

> On 30 Jan 2015, at 13:07, Alexander Lisachenko =
<lisachenko.it@gmail.com> wrote:
>=20
> Hello, internals!
>=20
> Today I was looking at PSR-7 and discovered this part of code:
>=20
> $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);
>=20
> 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 =
for
> 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 =
describing. 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 =
classes.

Thanks.
--
Andrea Faulds
http://ajf.me/