On Thu, Feb 20, 2020, at 8:47 AM, Levi Morrison via internals wrote:
> Just chiming in to voice strong support for this RFC. This is a key
> piece toward making PHP code statically analyzable. If it becomes
> required at the call site, such as in an edition of the language, it
> will significantly enhance the ability to reason about code and
> probably make it more correct as well. As a small example, consider
> this method on an Optional type class:
>
> function map(callable $f): Optional {
> if ($this->enabled) {
> return new Optional($f($this->data));
> } else {
> return $this;
> }
> }
>
> The intent is to return a new optional or an empty one, but if you
> pass a closure that accepts something by reference you can change the
> original, which is not intended at all. For people who defend against
> it, it requires saving `$this->data` to a local variable, then passing
> in the local. Then if the user does a call-by-reference it will affect
> the local, not the object's data.
If $this->data is itself an object, then you have a concern for data
manipulation (spooky action at a distance) even if it's passed by value. Given
how much data these days is objects, and thus the problem exists regardless of
whether it's by value or by reference passing, adding steps to make
pass-by-reference harder doesn't seem to help much.
--Larry Garfield
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