CODEWITHSUNDEEP
gogo-interface
Akhil Sasidharan
Akhil Sasidharan

Reputation: 29

Go interface: interface not implemented even though it is

Can someone explain to me why this kind of implementation is not allowed in go? I have a function that takes the interface the function is defined in as an argument. This throws an error.

package main

import (
    "fmt"
)

type Anode int

func (a Anode) IsLess(node Anode) bool { return a < node }

type Node interface {
    IsLess(node Node) bool
}

func test(a, b Node) bool {
    return a.IsLess(b)
}
func main() {
    a := Anode(1)
    b := Anode(2)
    fmt.Println(test(a, b))
}

Upvotes: 0

Views: 1847

Answers (1)

colm.anseo
colm.anseo

Reputation: 22147

The signatures are not the same. The argument types are different:

IsLess(Node) bool  // interface argument type is `Node` 
IsLess(Anode) bool // method argument type is `Anode`

To fix this - change your method to use argument type Node. You'll then need a Value() method to convert Anode into a comparable type (e.g. int):

func (a Anode) IsLess(node Node) bool { return a.Value() < node.Value() }
func (a Anode) Value() int            { return int(a) }

And add this to your interface definition:

type Node interface {
    IsLess(node Node) bool
    Value() int // <-- add this
}

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

Upvotes: 6

Related Questions