返回自身的接口（可克隆）

Question

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

Answer 1

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...