79 lines
1.5 KiB
Go
79 lines
1.5 KiB
Go
// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import "fmt"
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type printer interface {
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print()
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// use type assertion when you cannot change the interface.
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// discount(ratio float64)
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}
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type list []printer
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func (l list) print() {
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if len(l) == 0 {
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fmt.Println("Sorry. We're waiting for delivery 🚚.")
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return
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}
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for _, it := range l {
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it.print()
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}
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}
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// type assertion can extract the wrapped value.
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// or: it can put the value into another interface.
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func (l list) discount(ratio float64) {
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// you can declare an interface in a function/method as well.
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// interface is just a type.
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type discounter interface {
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discount(float64)
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}
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for _, it := range l {
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// you can assert to an interface.
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// and extract another interface.
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if it, ok := it.(discounter); ok {
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it.discount(ratio)
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}
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}
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}
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// ----
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// func (l list) discount(ratio float64) {
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// for _, it := range l {
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// // you can inline-assert interfaces
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// // interface is just a type.
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// g, ok := it.(interface{ discount(float64) })
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// if !ok {
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// continue
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// }
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// g.discount(ratio)
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// }
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// }
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// ----
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// // type assertion can pull out the real value behind an interface value.
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// // it can also check whether the value convertable to a given type.
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// func (l list) discount(ratio float64) {
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// for _, it := range l {
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// g, ok := it.(*game)
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// if !ok {
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// continue
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// }
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// g.discount(ratio)
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// }
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// }
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