update book code

eBook/exercises/chapter_11/map_function_interface.go

@@ -0,0 +1,62 @@
+package main
+
+import "fmt"
+
+type obj interface{}
+
+func main() {
+	// define a generic lambda function mf:
+	mf := func(i obj) obj {
+		switch i.(type) {
+			case int:
+				return i.(int) * 2
+			case string:
+				return i.(string) + i.(string)
+		}
+		return i
+	}
+	
+	isl := []obj{0, 1, 2, 3, 4, 5}
+	res1 := mapFunc(mf, isl)
+	for _, v := range res1 {
+		fmt.Println(v)
+	}
+	println()
+	
+	ssl := []obj{"0", "1", "2", "3", "4", "5"}
+	res2 := mapFunc(mf, ssl)
+	for _, v := range res2 {
+		fmt.Println(v)
+	}
+}
+
+func mapFunc(mf func(obj) obj, list []obj) ([]obj) {
+	result := make([]obj, len(list))
+	
+	for ix, v := range list {
+		result[ix] = mf(v)
+	}
+	
+	// Equivalent:
+	/*
+	for ix := 0; ix<len(list); ix++ {
+		result[ix] = mf(list[ix])
+	}
+	*/
+	return result
+}
+/* Output:
+0
+2
+4
+6
+8
+10
+
+00
+11
+22
+33
+44
+55
+*/