Today, did you know — a struct doesn’t have to implement an interface in Go. Go uses “duck typing”.
What is the duck typing?
If it looks like a duck, and it quacks like a duck, then it is a duck.
If it has a set of methods that match an interface, then you can use it wherever that interface is needed without explicitly defining that your types implement that interface.
Check out this interface:
// Speaker types can say things.
type Speaker interface {
Say(string)
}
Anything with a matching Say method can be called a Speaker.
We don’t do anything special to our struct types to satisfy this interface:
type Person struct {
name string
}
func (p *Person) Say(message string) {
log.Println(p.name+":", message)
}
Now assume we have a method that takes a Speaker:
func SpeakAlphabet(via Speaker) {
via.Say("abcdefghijklmnopqrstuvwxyz")
}
We can use our type look:
mat := new(Person)
mat.name = "Mat"
SpeakAlphabet(mat)
And imagine if another package exists that provides this type:
type SpeakWriter struct {
w io.Writer
}
func (s *SpeakWriter) Say(message string)
io.WriteString(s.w, message)
}
We could use that too — without the other package even knowing about our interface.
Reference: https://medium.com/@matryer/golang-advent-calendar-day-one-duck-typing-a513aaed544d