// Here's a basic interface for geometric shapes.
interface Geometry {
    double area()
    double perim()
}

// For our example we'll implement this interface on
// Rectangle and Circle classes.
class Rectangle implements Geometry {
    double width
    double height

    Rectangle(double width, double height) {
        this.width = width
        this.height = height
    }

    // To implement an interface in Groovy, we just need to
    // implement all the methods in the interface.
    double area() {
        return width * height
    }

    double perim() {
        return 2 * width + 2 * height
    }

    String toString() {
        "Rectangle(width: $width, height: $height)"
    }
}

class Circle implements Geometry {
    double radius

    Circle(double radius) {
        this.radius = radius
    }

    double area() {
        return Math.PI * radius * radius
    }

    double perim() {
        return 2 * Math.PI * radius
    }

    String toString() {
        "Circle(radius: $radius)"
    }
}

// If a variable has an interface type, then we can call
// methods that are in the named interface. Here's a
// generic measure function taking advantage of this
// to work on any Geometry.
def measure(Geometry g) {
    println g
    println g.area()
    println g.perim()
}

// Main execution
def r = new Rectangle(3, 4)
def c = new Circle(5)

// The Circle and Rectangle classes both
// implement the Geometry interface so we can use
// instances of these classes as arguments to measure.
measure(r)
measure(c)