On Wed, 30 Dec 2020, 20:27 Larry Garfield, <[email protected]> wrote:
>
> > > That's a good summary of why immutability and with-er methods (or some
> > > equivalent) are more ergonomic.
> > >
> > > Another point to remember: Because of PHP's copy-on-write behavior,
> full on
> > > immutability doesn't actually waste that much memory. It does use up
> some,
> > > but far less than you think. (Again, based on the tests MWOP ran for
> PSR-7
> > > a ways back.)
> >
> > I thought copy-on-write was only for arrays, not objects?
> >
> > Olle
>
> Copy on write applies to all values; the caveat is that with objects, the
> value being copied is the handle that points to an object in memory, rather
> than the object itself. That means passing an object by reference can do
> some seriously unexpected things, which is why you basically never do so.
>
> The point here is that if you have an object with 15 internal properties,
> it's memory usage is 15 zvals plus one zval for the object, plus one zval
> for the variable that points to it. (I'm over-simplifying here. A lot.)
> If you pass it to a function, only the one zval for the handle is
> duplicated, which is the same as for an integer.
>
> If you clone the object, you don't duplicate 15+1 zvals. You duplicate
> just the one zval for the object itself, which reuses the existing 15
> internal property entries. If in the new object you then update just the
> third one, PHP then duplicates just that one internal zval and modifies the
> new one. So you still are using only 18 zvals, not 36 zvals. (Engine
> people: Yes, I am *very* over-simplifying. I know.)
>
> Basically, what in most languages would require manually implementing
> "immutable data structures" we get for free in PHP, which is seriously
> sweet.
>
> The net result is that a with-er chain like this:
>
> $foo2 = $foo->withBar('x')->withBaz('y')->withBeep('z');
>
> is way, way less expensive than it looks, both on memory and CPU. It is
> more expensive than setters, but not by much.
>
Ok. You have a benchmark for this? I can make one otherwise, for the query
example.
It worries me a little that immutablility is pushed into the ecosystem as a
silver bullet. Main reason functional languages are using it is because
ownership is a newer concept, so it hasn't been adapted as much.
>
