Go "inheritance" - using anonymous type in a struct as a method parameter

Question

I'm trying to firm up the concept of inheritence that Go provides (rather "composition" than pure inheritence, perhaps). However, I'm failing to grasp why I can't use the "parent" type as a func parameter to produce a generic function that acts on the parameter.

package main

import "log"

type Animal struct {
    Colour string
    Name string
}

type Dog struct {
    Animal
}

func PrintColour(a *Animal) {
    log.Printf("%s\n", a.Colour)
}


func main () {
    a := new (Animal)
    a.Colour = "Void"
    d := new (Dog)
    d.Colour = "Black"

    PrintColour(a)
    PrintColour(d)
}

Assuming my understanding's incorrect, how can I achieve what I want in Go?

Edit Note:

• I don't want to attach the behaviour to the struct

• I'd like to keep the pointer type as the method parameter because I'm working separately on a pet project and this requires I manipulate the struct passed in before then acting on it.

• In reality my Dog struct would have additional fields/members; hopefully this doesn't muddy the water further

Answer 1

I like the answers here so far and I want to add one that allows you to do static type checking on the interface you pass in using an interface:

package main

import (
    "fmt"
)

type Animalizer interface {
    GetColour() string
}

type Animal struct {
    Colour string
    Name   string
}

type Dog struct {
    Animal
}

func (a *Animal) GetColour() string {
    return a.Colour
}

func PrintColour(a Animalizer) {
    fmt.Print(a.GetColour())
}

func main() {
    a := new(Animal)
    a.Colour = "Void"
    d := new(Dog)
    d.Colour = "Black"

    PrintColour(a)
    PrintColour(d)
}

On the playground

It will be possible to add further fields to Dog. The difference to Uriel's Answer is that calls to PrintColour will fail at compile time if something else than a struct implementing Animalizer is passed in.

Also you won't have to use a typeswitch since the compiler knows an Animalizer is implementing GetColour.

And, finally, the behaviour (printing) is separated from the struct, GetColour just returns the colour.