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Unfortunately, creating a constrained type like this isn't easy (or even doable) in all programming languages.

Fortunately, my preferred programming language, Raku, makes creating this sort of subset trivially easy[0]:

  subset UnitInterval of Real where 0 ≤ * ≤ 1
[0]: https://docs.raku.org/language/typesystem#index-entry-subset...



In C, I wonder if you could do something with functions and macros?

Say you need to represent velocity in a transportation simulation. You could have a function, velocity, that looks like this:

  double velocity(double v, char * of_what)
You use it to wrap constrained values. E.g.,

  double v_jogger = velocity(8.0, "human");
  double v_car = velocity(65.0, "city car");
velocity() simply returns the first argument, after doing validity checking based on the second argument.

You probably couldn't reasonably use this everywhere that you would use actual constrained types in a language that has them, but you could probably catch a lot of errors just using them in initializers.


The problem you'd have is that doing any operations on such a value could take it outside the bounds of the "type".


In Swift you can achieve this with Property Wrappers:

  @Clamping(0...14) var pH: Double = 7.0
https://nshipster.com/propertywrapper/#implementing-a-value-...


Is there a difference between ≤ and <= in Raku? Curious why you used ≤ in your example.


They're equivalent, Raku defines both Ascii compatible and Unicode names for typical operators. I expect they used ≤ because it looks nicer.


Yep, correct on both counts




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