refactor: common ifaces

interfaces/_old/09-stringer/main.go

@@ -0,0 +1,38 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func main() {
+	// The money type is a stringer.
+	// You don't need to call the String method when printing a value of it.
+	// var pocket money = 10
+	// fmt.Println(pocket)
+
+	store := list{
+		&book{product{"moby dick", 10}, toTimestamp(118281600)},
+		&book{product{"odyssey", 15}, toTimestamp("733622400")},
+		&book{product{"hobbit", 25}, toTimestamp(nil)},
+		&puzzle{product{"rubik's cube", 5}},
+		&game{product{"minecraft", 20}},
+		&game{product{"tetris", 5}},
+		&toy{product{"yoda", 150}},
+	}
+
+	store.discount(.5)
+
+	// The list is a stringer.
+	// The `fmt.Print` function can print the `store`
+	// by calling `store`'s `String()` method.
+	//
+	// Underneath, `fmt.Print` uses a type switch to
+	// detect whether a type is a Stringer:
+	// https://golang.org/src/fmt/print.go#L627
+	fmt.Print(store)
+}