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Date: Sun, 5 Nov 2017 16:44:15 -0800
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Subject: Re: [PHP-DEV] Constants and Access Modifiers
From: smalyshev@gmail.com (Stanislav Malyshev)

Hi!

> An abstract constant is a constant that requires its value to be defined
> later, like an abstract method that requires its implementation to be
> defined later.

It's not a constant then, and should be a method.

> 
> The thing is that I want something that CANNOT CHANGE. I want to require

You are contradicting yourself. If it is not known upfront, then it can
change - otherwise, you'd know it upfront. I'm not sure what you're
trying to do here, but I am getting pretty sure you shouldn't be doing
it with const's :)

> Dropping support for constant inheritance is imho also wrong from a pure
> logical point of view, since a constant's value is only constant if I
> refer to the very same constant. Meaning, the value of a constant in a
> subclass must not be the same value as the value in the superclass.
> 
>     class Integer extends Number {
>         public const MAX = \PHP_INT_MAX;
>         public const MIN = \PHP_INT_MIN;
>     }
> 
>     class WholeNumber extends Integer {
>         public const MIN = 0;
>     }
> 
>     class NaturalNumber extends WholeNumber {
>         public const MIN = 1;
>     }

Integer::MIN and NaturalNumber::MIN are different constants. So, it is
natural that they can have different values. Though using constants with
these names is slightly misleading, but if you always use full name, not
by much.

> does, simply because it is a different value. Of course we expect it to
> be compatible, they are after all in a tight relationship (inheritance).

Here you are getting into a dangerous territory, btw. Depending on your
modeling needs, of course, but your NaturalNumber can violate contract
of Integer, such as "being able to represent -10". Thus, inheritance
could be wrong way to do it, at least in the way you described above.
One has to be very careful with which exactly contract are you modelling
- inheritance is not just shortcut for avoiding copy-paste.

> I mentioned Dart in the initial message, they have a much richer
> understanding of const than we have it in PHP. Maybe this also helps to
> broaden your views on the topic:
> 
> https://news.dartlang.org/2012/06/const-static-final-oh-my.html

From this link, it looks like const in Dart has pretty much nothing in
common with const in PHP, besides name, so in the interest of avoiding
confusion, I would not discuss it in the same topic.

-- 
Stas Malyshev
smalyshev@gmail.com