update: powerdrawer interface

interfaces/04-interfaces/power/socket.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"
+	"math/rand"
+)
+
+// PowerDrawer represents an electrical device that can draw power.
+// The power source doesn't have to be a Socket.
+type PowerDrawer interface {
+	Draw(power int)
+}
+
+// Socket has the power!
+type Socket struct {
+	power int
+}
+
+// Plug a device to draw power from the `Socket`
+func (s *Socket) Plug(device PowerDrawer) error {
+	n := rand.Intn(50) + 1
+
+	if s.power-n <= 0 {
+		return fmt.Errorf("socket is out of power for %dkW", n)
+	}
+
+	s.power -= n
+	device.Draw(n)
+
+	return nil
+}