Infinite loop with by name value classes

[nicolasstucki]

class Foo(sc: => Int) extends AnyVal

emits the error

2 |  class Foo(sc: => Int) extends AnyVal
  |        ^
  |        value sc in class Foo does not take parameters

but then stays in an infinite loop.

In scalac it fails with

Foo.scala:2: error: value class parameter must be a val and not be private[this]

In both scalac and dotty

class Foo(val sc: => Int) extends AnyVal

fails correctly with val parameters may not be call-by-name

[allanrenucci]

Do we want to forbid this? dotc does not require value class parameter to be a val as opposed to scalac

[nicolasstucki]

Forbid what exactly?

[allanrenucci]

Something like this:

class Foo(sc: => Int) extends AnyVal

The following of course should be forbidden:

class Foo(val sc: => Int) extends AnyVal

But that's already the case

[nicolasstucki]

Then yes because the first one is a shorthand of the second

[allanrenucci]

Then yes because the first one is a shorthand of the second

Then by this argument class Foo(sc: => Int) should be forbidden because it is a shorthand of class Foo(val sc: => Int)?

Also, it is not true. It would be the shorthand for

class Foo(private[this] val sc: => Int) extends AnyVal

if you could write that in source

[nicolasstucki]

You are right. It feels like it should not be allowed because it would not have value semantics.

[nicolasstucki]

I asked @sjrd and he said "just don't, disallow it".