Using the same type class twice collapses to a single concrete type

[panno8M]

Nim Version

v2.2.4
v2.3.1 (devel #d60e021)

Description

When I try to define a generic type that takes two parameters constrained by the same type class (either a concept or a union type), compilation fails in cases that I would expect to work.

type
  Concept = concept x
    $x is string
  TypeClass = int | float

  ConceptObject[A: Concept; B: Concept] = object
  TypeClassObject[A: TypeClass; B: TypeClass] = object

# ok
var a: ConceptObject[int, int]
var b: TypeClassObject[int, int]

# error
var c: ConceptObject[int, float]
var d: TypeClassObject[int, float]

Current Output

Error: cannot instantiate ConceptObject [type declared in PATH(6, 3)]

got: <typedesc[int], typedesc[float]>
but expected: <A: Concept, B: Concept>



Error: cannot instantiate TypeClassObject [type declared in PATH(7, 3)]

got: <typedesc[int], typedesc[float]>
but expected: <A: TypeClass, B: TypeClass>

Expected Output

Known Workarounds

If I wrap one of the type classes in another concept, or define a duplicate type class, or use an inline union in the generic parameters, then it works as expected.

type
  Concept2 = concept type T
    T is Concept
  ConceptObject2[A: Concept; B: Concept2] = object

assert compiles(ConceptObject2[int, float])

type
  TypeClass2 = int | float
  TypeClassObject2[A: TypeClass; B: TypeClass2] = object

assert compiles(TypeClassObject2[int, float])

type
  TypeClassObject3[A: int|float; B: int|float] = object

assert compiles(TypeClassObject3[int, float])

Additional Information

I am not sure whether this is a compiler bug or simply a misuse on my side.

[Graveflo]

fwiw this also compiles:

type
  Concept = concept
    proc `$`(x: Self): string
  ConceptObject[A: Concept; B: Concept] = object

# ok
var a: ConceptObject[int, int]
# error
var c: ConceptObject[int, float]