add: summaries iface

interfaces/09-little-refactor/main.go

@@ -17,3 +17,18 @@ func main() {
 	l.discount(.5)
 	l.print()
 }
+
+/*
+Summary:
+
+- Prefer to work directly with concrete types
+  - Leads to a simple and easy to understand code
+  - Abstractions (interfaces) can unnecessarily complicate your code
+
+- Separating responsibilities is critical
+  - Timestamp type can represent, store, and print a UNIX timestamp
+
+- When a type anonymously embeds a type, it can use the methods of the embedded type as its own.
+ - Timestamp embeds a time.Time
+ - So you can call the methods of the time.Time through a timestamp value
+*/