“A type parameter with the comparable constraint accepts as a type argument any comparable type. It permits the use of == and != with values of that type parameter”

I think that’s an unfortunate choice. Quite a few other languages use the term equatable for that, and have comparable for types that have =, ≤ and similar defined. Using comparable here closes the door for adding that later.

I also find it unfortunate that they chose

  type SignedInteger interface {
    type int, int8, int16, int32, int64
  }

as that means other libraries cannot extend the set of types satisfying the constraint.

One couldn’t, for example, have one’s biginteger class reuse a generic gcd or lcm function.