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Improve handling of untyped polymorphed classes about chimney HOT 2 CLOSED

cupuyc commented on August 16, 2024

Improve handling of untyped polymorphed classes

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Comments (2)

krzemin commented on August 16, 2024

I'm keen to explore what is the limitation here.

Let's define minimal example in REPL:

scala> case class Source(name: String, poly: String)
defined class Source

scala> case class Target[T](name: String, poly: T)
defined class Target

scala> val src = Source("name", "test")
src: Source = Source(name,test)

Trying to construct instance with passing wildcard as a type argument ends up with:

scala> Target[_](src.name, src.poly)
<console>:15: error: unbound wildcard type
       Target[_](src.name, src.poly)
              ^
// adding a bound to wildcard doesn't seem to help either

scala> Target[_ <: String](src.name, src.poly)
<console>:15: error: unbound wildcard type
       Target[_ <: String](src.name, src.poly)
              ^

However if we construct an object using new, we get slightly different error:

scala> new Target[_](src.name, src.poly)
<console>:15: error: class type required but Target[_] found
       new Target[_](src.name, src.poly)
           ^
scala> new Target[_ <: String](src.name, src.poly)
<console>:15: error: class type required but Target[_ <: String] found
       new Target[_ <: String](src.name, src.poly)
           ^

I didn't verify this, but my intuition is that chimney already generates code like this, but this fails at type checking after macro expansion. Note the error you're getting is the same as in version with new (chimney generates code with new to construct objects).

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krzemin commented on August 16, 2024

Closed due to inactivity.

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