Add RuntimeConstraint

[kyri-petrou]

POC for #174

[Iltotore]

The POC is ok to me. You'll just need to do the same changes in modules' RefinedTypeOps extension (like cats and zio).

[Iltotore]

Why does it need to have a third T type parameter?

[kyri-petrou]

This type parameter is required for opaque types so one can do something alongside what's below. It seems that the unnecessary type param was C in this case

object One {
  opaque type Foo = Int :| GreaterEqual[10]
  object Foo extends RefinedTypeOpsImpl[Int, GreaterEqual[10], Foo]
}

object Two {
  import One.Foo
  def doSomething(a: Int)(using RuntimeConstraint[Int, Foo]): Foo = ???
}

[Iltotore]

I don't see why it should have a different shape than Constraint[A, C]:

final class RuntimeConstraint[A, C](_test: A => Boolean, val message: String):
  inline def test(value: A): Boolean = _test(value)

trait RefinedTypeOpsImpl[A, C, T](using rtcAuto: RuntimeConstraint.AutoDerived[A, C]):
  ???

For notes about AutoDerived, see my other reply below.

[kyri-petrou]

My initial thinking was so that we could use it for opaque types outside of the opaque type companion object. However, thinking about it a bit more now I don't think that makes too much sense. I changed it as per your suggestion

[kyri-petrou]

One of the things that was bugging me was having auto-derivation of RuntimeConstraint from a Constraint enabled by default. This is fairly dangerous as methods requiring a RuntimeConstraint would auto-derive one if one wasn't in scope, which can lead to increased compilation time and generated code size.

With this, a user / method / etc can define whether they want an explicit or implicit given to be provided. For newtypes, this is generated by default

Example:

// will raise a compile-time error if one isn't explicitely defined (newtypes are OK since we create one for them in RefinedTypeOpsImpl)
def foo(value: Int)(using RuntimeConstraint[Int, Int :| Greater[10]]) = ??? 

 // Will prioritise an explicitly defined RuntimeConstraint and auto-derive one if it doesn't exist
def foo(value: Int)(using RuntimeConstraint.AutoDerived[Int, Int :| Greater[10]]) = ???

[Iltotore]

I still don't understand why RuntimeConstraint does not have the same type parameters than Constraint. Then, it would look like:

def foo(value: Int)(using RuntimeConstraint[Int, Greater[10]]) = ???

def foo(value: Int)(using RuntimeConstraint.AutoDerived[Int, Greater[10]]) = ???

Also, I'm not sure about the usefulness of AutoDerived. It would leak an implementation detail (how the instance is generated) and I'm not sure about the real impact of auto deriving automatically on bytecode size and compilation times.

[kyri-petrou]

After sleeping on it, I think you're right. I reverted these changes

[Iltotore]

I don't think we need such given instance. If someone want to get the constraint bound to a newtype, it can do it as follow:

inline def foo[T](using mirror: RefinedTypeOps.Mirror[T], constraint: Constraint[mirror.BaseType, mirror.ConstraintType] /*Or runtime constraint*/) = ???

But we can get rtc as a public val to allow using it in RefinedTypeOps extensions like in Cats or ZIO

[kyri-petrou]

I made it a val but also created a protected given RuntimeConstraint[A, C]. My reasoning behind having the protected given is so that it can be used in the companion object of opaque types when creating codecs etc

[Iltotore]

Miss clicked on "approve". I'm changing it to "request changes"

Miss clicked on "approved"

[Iltotore]

Looks good to me. Can you add some Scaladoc to RuntimeConstraint?

[kyri-petrou]

Looks good to me. Can you add some Scaladoc to RuntimeConstraint?

Done. Feel free to merge in if you're happy with it!