Add example of struct embedding in Go

Also mention implementing interfaces with embedding

Fixes #381
Fixes #398

examples/embedding/embedding.go

@@ -0,0 +1,59 @@
+// Go support _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)
+}
+
+// A `container` _embeds_ a `base`. An embedding looks
+// like a field without a name.
+type container struct {
+	base
+	str string
+}
+
+func main() {
+
+	// When creating structs with literals, we have to
+	// initialize the embedding explicitly; here the
+	// embedded type serves as the field name.
+	co := container{
+		base: base{
+			num: 1,
+		},
+		str: "some name",
+	}
+
+	// We can access the base's fields directly on `co`,
+	// e.g. `co.num`.
+	fmt.Printf("co={num: %v, str: %v}\n", co.num, co.str)
+
+	// Alternatively, we can spell out the full path using
+	// the embedded type name.
+	fmt.Println("also num:", co.base.num)
+
+	// Since `container` embeds `base`, the methods of
+	// `base` also become methods of a `container`. Here
+	// we invoke a method that was embedded from `base`
+	// directly on `co`.
+	fmt.Println("describe:", co.describe())
+
+	type describer interface {
+		describe() string
+	}
+
+	// Embedding structs with methods may be used to bestow
+	// interface implementations onto other structs. Here
+	// we see that a `container` now implements the
+	// `describer` interface because it embeds `base`.
+	var d describer = co
+	fmt.Println("describer:", d.describe())
+}

examples/embedding/embedding.hash

@@ -0,0 +1,2 @@
+8a15291c6e82b9c6873002e2aa5cef65907a3405
+Xtg07j06zBv

examples/embedding/embedding.sh

@@ -0,0 +1,5 @@
+$ go run embedding.go
+co={num: 1, str: some name}
+also num: 1
+describe: base with num=1
+describer: base with num=1