Re: Analysis of property visibility, immutability, and cloning proposals

2020-12-30 19:50 GMT, Olle Härstedt <olleharstedt@gmail.com>: > On Wed, 30 Dec 2020, 20:27 Larry Garfield, <larry@garfieldtech.com> 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. Tiny benchmark here: https://gist.github.com/olleharstedt/eaaf1dd40be541f84aa0f3954a0ea54a Running this on my ARM machine with PHP 7.2 gives ~1.2s for the immutable loop, ~0.35s for the mutable one, meaning immutability is ~3x as expensive performance wise. And this is for a SMALL object - I suspect the performance hit will grow the bigger the class gets (more properties to clone). Correct me if I'm wrong. :/ Olle