documentation for methods and interfaces

go/02-next-level/00-methods.go

@@ -6,12 +6,14 @@ type Counter struct {
 	value int
 }
 
-// pointer receiver
+// pointer receiver. The method operates directly on the object c points to
+// Use a pointer receiver whenever the object needs to be modified.
 func (c *Counter) Increment() {
 	c.value++
 }
 
-// value receiver
+// value receiver. The method operates on copy of object c. Use a value
+// receiver when the object does not need to be modified in the method.
 func (c Counter) String() string {
 	return fmt.Sprintf("Counter value: %d", c.value)
 }

go/02-next-level/01-interfaces.go

@@ -14,12 +14,14 @@ type rect struct {
 	width, height float64
 }
 
+// Ensure that rect implements the geometry interface
 var _ geometry = rect{}
 
 type circle struct {
 	radius float64
 }
 
+// Ensure that circle implements the geometry interface
 var _ geometry = circle{}
 
 func (r rect) area() float64 {
@@ -36,12 +38,16 @@ func (c circle) perim() float64 {
 	return 2 * math.Pi * c.radius
 }
 
+//Metods demonstrates how to use an interface
 func measure(g geometry) {
 	fmt.Println(g)
 	fmt.Println(g.area())
 	fmt.Println(g.perim())
 }
 
+
+//Method demonstrates casting an interface to a concrete type. 
+//Should be avoided in practice whenever possible.
 func detectCircle(g geometry) {
 	if c, ok := g.(circle); ok {
 		fmt.Println("circle with radius", c.radius)