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Date: Sun, 1 Feb 2015 01:06:48 +0000
Cc: Larry Garfield <larry@garfieldtech.com>,
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To: Stanislav Malyshev <smalyshev@gmail.com>
Subject: Re: [PHP-DEV] [RFC] Immutable variables and objects
From: ajf@ajf.me (Andrea Faulds)

Hi Stas,

> On 1 Feb 2015, at 00:55, Stanislav Malyshev <smalyshev@gmail.com> =
wrote:
>=20
>=20
>> The with*() methods in PSR-7 are documented to return a new instance,
>> not modify the existing instance.  Yes, there's no way in PHP itself =
to
>> force that syntactically, which is why documentation exists. :-)
>>=20
>> Also, in the benchmarks we've run the performance cost of all those =
new
>> objects is measured in nanoseconds, ie, small enough that we're not
>> worried about it.  (Hats off to the PHP Internals folks for making =
that
>> fast!)
>=20
> It is great that this is fast, but I wonder (maybe off-topic?) why do
> it? I.e. it is clear that in something like:
>=20
> $a =3D new Request->withHeaders(...)->withBody(...)
> ->withEncoding(...)->withETag(...)
>=20
> the intermediate objects are useless and nobody needs 5 new objects =
when
> you do it. Am I missing something here?

I assume the reason for doing this is so you can=E2=80=99t ever modify =
the object from a distance, you must always create a new one to avoid =
messing up anything with an existing handle on it.

As you mention, though, this means that you get useless intermediate =
objects. This use case could be solved much better if we had =
copy-on-write/value-type classes like PHP 4 had. If Request was a =
value-type class, then you could do this:

    $a =3D new Request();
    $a->addHeaders(=E2=80=A6);
    $a->setBody(=E2=80=A6);
    $a->setEncoding(=E2=80=A6);
    $a->setETag(=E2=80=A6);

Here, there=E2=80=99s no redundant objects made, but if you pass $a on, =
it=E2=80=99d be automatically copied by PHP, so you don=E2=80=99t need =
to worry about it being modified.

Would that make sense? It=E2=80=99s no different than how our existing =
value types like scalars and arrays work.
--
Andrea Faulds
http://ajf.me/