go by example part 3

5-go-by-example/21-embedding.go

@@ -0,0 +1,48 @@
+// embedding of structs and interfaces to express a more seamless composition of types
+
+package main
+
+import "fmt"
+
+type base struct {
+	num int
+}
+
+func (b base) describe() string {
+	return fmt.Sprintf("base with num=%v", b.num)
+}
+
+// container embeds a base
+// embedding looks like a field without a name
+type container struct {
+	base
+	str string
+}
+
+func main() {
+	// when creating structs with literals, initialize the embedding explicitly
+	co := container{
+		base: base{
+			num: 1,
+		},
+		str: "some name",
+	}
+
+	// access the base’s fields directly
+	fmt.Printf("co={num: %v, str: %v}\n", co.num, co.str)
+
+	// full path using the embedded type name
+	fmt.Println("also num:", co.base.num)
+
+	// container embeds base
+	// methods of base also become methods of a container
+	fmt.Println("describe:", co.describe())
+
+	type describer interface {
+		describe() string
+	}
+
+	// container implements describer interface because it embeds base
+	var d describer = co
+	fmt.Println("describer:", d.describe())
+}