learngo/interfaces/06-empty-interface/list.go

// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
// For more tutorials  : https://learngoprogramming.com
// In-person training  : https://www.linkedin.com/in/inancgumus/
// Follow me on twitter: https://twitter.com/inancgumus

package main

import "fmt"

type printer interface {
	print()
}

type list []printer

func (l list) print() {
	if len(l) == 0 {
		fmt.Println("Sorry. We're waiting for delivery 🚚.")
		return
	}

	for _, it := range l {
		it.print()
	}
}

func (l list) discount(ratio float64) {
	type discounter interface {
		discount(float64)
	}

	for _, it := range l {
		if it, ok := it.(discounter); ok {
			it.discount(ratio)
		}
	}
}