CaseClass - helper to provide the `copy` method

[jatcwang]

Hello, thank you for the fantastic library!

Typeclasses that modify a case class instances will need to call the copy method. Given there are quite a few edge cases to handle, perhaps Hearth can add a helper for it? Let me know your thoughts and I'll take a stab at the implementation.

Describe the desired behavior

Add a helper method on hearth.typed.Classes.CaseClass so macro code can easily obtain reference to copy

lazy val copyMethod: Option[Method.OfInstance[A, A]] = ...

Implementation:

• Only returns the "canonical" copy method, which has a parameter list that matches the case class primary constructor parameters
  • edge cases like case class Boo(i: Int)(s: Int) need to be handled too
• If the right copy method cannot be found (e.g. sealed abstract case class), return None

Use case example

val cc: CaseClass[A] = CaseClass.parse[A].toOption.getOrElse(..)
val copyMethod = cc.copyMethod.getOrElse(..)

val ccInstance: Expr[A] = ..
val args: Arguments = ...

copyMethod.apply(ccInstance, args)

How it relates to existing features

Currently user can use Method.methodsOf[A].find(_.value.name == "copy"), but all edge cases will need to be handled by the user

Other considerations

• Need to deal with public/private copy methods. Perhaps add a copyMethodPublic which is the most common use case?

[MateuszKubuszok]

Hey 👋

Thanks for the suggestion. I guess we can add a copy method utility like e.g.

def copy(accessible: Accessible = AtCallSite): Option[Method.OfInstance[A, A]] = ...