返回自身的接口（可克隆）

I'm trying to create a cloneable interface and am running into some problems getting structs to implement the interface. It appears this is a limit of go which isn't in many other langauges. I'm trying to understand the justification for this limit.

var _ Cloneable = test{}

type Cloneable interface {
    Clone() Cloneable
}

type test struct {
}

func (t *test) Clone() *test {
    c := *t
    return &c
}

Playground: https://play.golang.org/p/Kugatx3Zpw

Followup question since it still seems weird to me. This also does not compile

var _ Cloneable = &test{}

type Cloneable interface {
    Clone() Cloneable
}

type Cloneable2 interface {
    Clone() Cloneable2
}

type test struct {
}

func (t *test) Clone() Cloneable2 {
    c := *t
    return &c
}

Playground: https://play.golang.org/p/jlyMDPF1WB

I found this thread which talks about it and the answer seems to be supporting covariant function types would make the language harder to understand for little benefit. https://github.com/golang/go/issues/7512

At least they made a conscious decision to not support a feature supported by most other languages. I don't really buy it, but oh well...

To satisfy an interface method, the argument and return types must use the same types used in the interface declaration. The Clone method must return a Cloneable to satisfy the interface:

func (t *test) Clone() Cloneable {
  c := *t
  return &c
}

The Clone method cannot return a *test or Cloneable2 because these types are not the Cloneable type.

The pointer type implements the interface:

var _ Cloneable = &test{}

Because the test type must satisfy the Cloneable interface for the Clone method to compile, this compile time assertion is not needed.

playground example

(The question is a moving target. This is an answer to two previous edits of the question.)