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
+*/

interfaces/10-stringer/main.go

@@ -32,3 +32,17 @@ func main() {
 	// var pocket money = 10
 	// fmt.Println("I have", pocket)
 }
+
+/*
+Summary:
+
+- fmt.Stringer has one method: String()
+  - That returns a string.
+  - It is better to be an fmt.Stringer instead of printing directly.
+
+- Implement the String() on a type and the type can represent itself as a string.
+  - Bonus: The functions in the fmt package can print your type.
+  - They use type assertion to detect if a type implements a String() method.
+
+- strings.Builder can efficiently combine multiple string values.
+*/