github.com/pciet/unordered with https://github.com/golang/go/issues/15292#issuecomment-359347858

generic_unordered.go

// wins for container types is compile-time type check without a wrapper type
// but now a Value() method is required on the contained item interface instead of using a type assertion

type Comparable interface {
  Equal(Ť) bool
  Value() Ť
}

type EqualSet []Comparable

func (an EqualSet) Remove(the Comparable) EqualSet {
  out := make(EqualSet, 0, len(an))
  found := false
  for _, item := range an {
    if found==false && item.Equal(the) {
      found = true
      continue
     }
     out = out.Add(item)
  }
  return out
}

// no need for "return CoordinateSet(EqualSet(inputcoordinateset).Remove(coordinate))" method

type Coordinate struct {
  X int
  Y int
}

func (the Coordinate) Equal(to Coordinate) bool {
  if the == to {
    return true
  }
  return false
}

func (the Coordinate) Value() Coordinate {
  return the
}

func main() {
  set := make(EqualSet, 8)
  for i := 0; i < 8; i++ {
    set[i] = Coordinate{i, i}
  }
  totalX := 0
  for _, x := range set {
    // before this would be a type assertion instead of a required Value() method on the interface
    totalX += x.Value().X
  }
  fmt.Println(totalX)
  fmt.Println(set.Remove(Coordinate{2, 2}))
}