update book code

eBook/examples/chapter_10/methodset1.go

@@ -0,0 +1,22 @@
+// methodset1.go
+package main
+
+import (
+	"fmt"
+)
+
+type List []int
+func (l List) Len() int { return len(l) }
+func (l *List) Append(val int) { *l = append(*l, val) }
+
+func main() {
+	  // A bare value
+        var lst List
+        lst.Append(1)
+        fmt.Printf("%v (len: %d)\n", lst, lst.Len()) // [1] (len: 1)
+
+        // A pointer value
+        plst := new(List)
+        plst.Append(2)
+        fmt.Printf("%v (len: %d)\n", plst, lst.Len()) // &[2] (len: 1)
+}