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Date: Wed, 30 Dec 2020 13:30:48 -0600
To: "php internals" <internals@lists.php.net>
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Subject: =?UTF-8?Q?Re:_[PHP-DEV]_Analysis_of_property_visibility,_immutability,_a?=
 =?UTF-8?Q?nd_cloning_proposals?=
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Dec 30, 2020, at 12:42 PM, Olle H=C3=A4rstedt wrote:

> A more motivating example for uniqueness is perhaps a query builder.
>=20
> ```
> $query =3D (new Query())
>   ->select(1)
>   ->from('foo')
>   ->where(...)
>   ->orderBy(..)
>   ->limit();
> doSomething($query);
> doSomethingElse($query);
> ```
>=20
> In the above snippet, we don't know if doSomething() will change
> $query and cause a bug. The issue can be solved with an immutable
> builder, using withSelect(), withWhere(), etc, OR it's solved with
> uniqueness, forcing a clone to avoid creating a new alias (passing
> $query to a function creates an alias inside that function). The
> optimisation is the same as in my previous example, avoiding copying
> $query multiple times during build-up.

For a query builder, I probably wouldn't make it immutable anyway, mysel=
f.  If you really want to force that doSomething() cannot modify the obj=
ect that is otherwise mutable, calling doSomething(clone $query) already=
 works today and gets that net effect, provided that Query is safe to cl=
one.  (Vis, has no service dependencies, and if it has any dependent val=
ue objects then it has a __clone() method that deep clones.)

> >> The guarantee in both above snippets is that myfun() DOES NOT modif=
y
> >> $b before returning it. BUT with immutability, you have to copy $b
> >> three times, with uniqueness only one.

Yes, but with CoW those 3 copies are not that expensive, so we can most =
of the time ignore them except as a very micro-optimization.  (See previ=
ous email.)

--Larry Garfield