method with singleton type mismatches same singleton type

As the below example shows, a method that takes a singleton type Int(1) cannot be applied with 1.

scala> def id(x: 1): 1 = x
id: (x: Int(1))Int(1)
scala> id(1)
-- [E007] Type Mismatch Error: <console> -----------------------------------
6 |id(1)
  |   ^
  |   found:    Int(1)
  |   required: Int(1)
  |

[rethab]

I have analyzed this a little.

What I have noticed is that in Typer.scala:1841 where the types are compared

else if (tree.tpe <:< pt) {

it returns false when my code from the first example is run in the REPL, but it returns true if the example from @liufengyun is run (ie. w/o REPL).

Actually, in both cases both sides are equal (ConstantType(Constant(4))) however in the REPL, the two don’t refer to the same object in memory whereas otherwise they do. It seems that the TypeComparer doesn’t return true unless they point to the same object in memory.

My assumption is that the types are usually cached, but not between runs in the REPL. This is supported by the following snippet, which works in the REPL:

scala> def id(x: 4): 4 = x; id(4)
def id(x: 4.type): Int(4)

What I am unsure about is whether all types are always supposed to be cached and therefore the REPL needs to ensure that it re-uses types between runs (ie. several evaluated lines) or the TypeComparer should return true in topLevelSubType if they are the same but don’t point to the same object.

[rethab]

Thanks a lot! I’m actually mostly using the debugger to step through and try to make sense out of it 😃