This question is frequently asked
<https://golang.org/doc/faq#t_and_equal_interface>. In short: Because the
arguments to myType.Less have to be of type Compare, not myType. Go does
not have polymorphic types.
To answer the "how should this be done in Go the right way": IMO the answer
is "not". The only way to do it, is to use Compare in the individual
methods and type-assert:
func (t myType) Less(i, j Compare) bool {
return i < j
}
But to me, wanting to do this seems to indicate the wrong abstraction. What
is it, you are actually trying to solve?
You can also have a look at how the sort package
<https://godoc.org/sort#Interface> solves a similar problem.
On Tue, Nov 21, 2017 at 2:39 PM, <christian.b.muel...@gmx.net> wrote:
> hi there,
>
> and first of all sorry that i couldn't find the answer by myself here. I
> tried to improve some of my code with general interface definitions. They
> should work like macros for different types of variables. Here is my
> reduced example and the question - how should this be done in go the right
> way?
>
> thanx a lot,
> c.
>
> Code hier eingeben...
> package main
>
> import "fmt"
>
> func main() {
> // test
> fmt.Println(Eq(myType(5), myType(5)))
> // gives me ...
> /*
> * ./main.go:7:23: cannot use myType(5) (type myType) as type
> Compare in argument to Eq:
> * myType does not implement Compare (wrong type for Less
> method)
> * have Less(myType, myType) bool
> * want Less(Compare, Compare) bool
> */
> }
>
> // define my custom type
> type myType int
> // and satisfy the interface
> func (t myType) Less(i, j myType) bool {
> return i < j
> }
>
> // the interface condition
> type Compare interface {
> Less(i, j Compare) bool
> }
> // functions when satisfied
> func Ls(i, j Compare) bool {
> return i.Less(i, j) }
> func Gt(i, j Compare) bool {
> return i.Less(j, i) }
> func GtEq(i, j Compare) bool {
> return !i.Less(i, j) }
> func LsEq(i, j Compare) bool {
> return !i.Less(j, i) }
> func Nt(i, j Compare) bool {
> return i.Less(i, j) || j.Less(j, i) }
> func Eq(i, j Compare) bool {
> return !Nt(i, j) }
>
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