Overloading operators shadows the built-in ones

[kyouko-taiga]

Overloading a built-in operator (e.g. +) in a user module shadows the built-in definitions of the same operator, making it impossible to manipulate built-in values.

Here's a minimal example:

type Point :: #point(x: Int, y: Int)
func + (_ lhs: Point, _ rhs: Point) -> Point ::
  #point(x: lhs.x + rhs.x, y: lhs.y + rhs.y)

The above code will produce a type error complaining that #point(x: Int, y: Int) does not match type Int, suggesting that the operator + between integers is no longer considered by the type solver. Further evidences can be found by observing the type constraints generated by the above program, which do not feature any disjunction.