Struct does not implement interface if it has a function which parameter implement interface

Question

I have a package in which I have two interfaces

package main
type A interface {
    Close()
}
type B interface {
    Connect() (A, error)
}

I h

Answer 1

The returned type for your Connect method should be A and not *C.

The way you defined the Connect method is that it should return an interface, not a specific type. You will still be able to return *C as it implements the A interface.

package main

type A interface {
    Close()
}

type B interface {
    Connect() (A, error)
}

type C struct {
}

func (c *C) Close() {
}

type D struct {
}

func (d *D) Connect() (A, error) {
    c := new(C)
    println("successfully created new C:", c)
    return c, nil
}

func test(b B) {
    b.Connect()
}

func main() {
    d := new(D)
    test(d)
}

Outputs

successfully created new C: 0xe28f0

Try it out yourself here