This is one of the most interesting things about Go: Interfaces.
Intro
If quacks like a duck. Then it is a duck.
This features really bothered me in Java. Every class that I need to implement an interface, I need to declare which interface that I am going to implement.
In Go, this is different. If a struct has a method implementing an interface, than it is already done.
Structs
Lets create some structures:
type Square struct {
X float64
}
type Rectangle struct {
X, Y float64
}
Interface
Now we want to calculate the area and print it. So each one need to have an interface called Area():
type IArea interface {
Area() float64
}
And then we implement it:
func (s Square) Area() float64 {
return s.X * s.X
}
func (r Rectangle) Area() float64 {
return r.X * r.Y
}
Using it
So, to use each one to print:
func PrintArea(area IArea) {
fmt.Println(area.Area())
}
func main() {
square := Square{X: 2.0}
rectangle := Rectangle{X: 2.0, Y: 4.0}
PrintArea(square)
PrintArea(rectangle)
}
If you try to use some structure without implementing the interface, the compiler gives an error:
type Triangle struct {
height, base float64
}
func main() {
square := Triangle{height: 2.0, base: 3.0}
PrintArea(triangle)
}
cannot use rectangle (type Triangle) as type IArea in argument to PrintArea:
Triangle does not implement IArea (missing Area method)