Re: Typed constants revisited

On Thu, Mar 24, 2022, at 11:34 AM, Mark Niebergall wrote: > Pierre, > > On Thu, Mar 24, 2022 at 9:20 AM Pierre <pierre-php@processus.org> wrote: > >> Le 24/03/2022 à 16:06, Mark Niebergall a écrit : >> > So you are correct, the const value does have a value that has a type, >> but >> > there is no way to enforce which type the value is or to use const with >> > inheritance, which is part of the bigger picture here. >> >> That was exactly my point: the type could simply implicitely be the one >> of the original value. >> >> Then the engine just has to use the existing covariance/contravariance >> rules for type checks based upon the guessed value type. This would fix >> the type safety issue you are referring to. >> > > I'd rather not use the "guessed value type" in code, that tends to lead to > bugs: guessing = bugs. Explicitly declaring the type avoids the pitfalls of > guessing and ensures code predictability. It also comes with added > benefits, including self-documenting code, defined inheritance requirements > (the way you describe would have BC breakage), and (for some IDEs) type > hinting. > > Of note, many other languages already have typed constants. Yes this is the > "everyone else is doing it" argument, but they had their valid reasons. > Some are strong typed languages, others are not. See: > > - Go: https://go.dev/blog/constants > - HVVM: https://docs.hhvm.com/hack/classes/type-constants > - C: https://fresh2refresh.com/c-programming/c-constants/ > - C++: https://en.cppreference.com/w/c/language/const > - C#: > > https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/const The addition of union types put the kibosh on successfully type guessing, I think. If you have a const that you'll allow a float or int in, and the default is 0, the guesser will guess int, not float, and then you can't allow a float. So "constant inheritance" is a use case for typed constants, even if constant inheritance is a rather edge-case situation to begin with. --Larry Garfield