On Thu, Apr 4, 2024 at 2:19 PM Barney Laurance <bar...@redmagic.org.uk> wrote:
> > I don't think it will be possible to make a good Money class as a child of > this. BcNum is a read-only class, so if the constructor of BcNum is final > then the child class won't be able to take the currency as a constructor > param, and won't be able to protect the invariant that currency must be > initialized. If the constructor of BcNum were made non-final then BcNum > wouldn't be able to protect the invariant of the numeric value always being > initialized once the constructor has returned. And it should be > straightforward to make a good money class as a composition of BcNum and a > currency enum or string. > > The RFC does not list the constructor as final, and I would not expect it to. > There's probably not any good use case for a subclass to add properties, > unless perhaps the subclass developers are willing do do away with some of > the checks that would normally be done on a value object by the PHP runtime > to keep it valid (maybe replacing them with static analysis checks). But > there are lots of reasonable use cases for subclasses to add methods, even > if they're effectively syntax sugar for static methods with a BcNum typed > param. > > I literally just provided in the quote you are replying to a good use case for a subclass. You can do the same thing with composition yeah, and that might even be better to a lot of people, but I don't think this RFC should take a position AGAINST subclasses and in favor of composition. > Having just written that I've now checked the behavior of DateTime - see > https://3v4l.org/5DQZg . The constructor of that isn't final, so a child > class can replace it with an empty constructor. But if it does that and > leaves the value uninitialized then it blows up on a call to `format`. > That's probably not something we should emulate. DateTimeImmutable behaves > the same way. > Why not? Writing something like that obviously does not work, and the error would be immediately apparent. Is it possible to create something that will error? Of course. That's not an error that needs to be aggressively guarded against, because the feedback is rapid and obvious. Jordan
