Add code

4-empty-interface-in-go/Makefile

@@ -0,0 +1,2 @@
+all:
+	go run main.go

4-empty-interface-in-go/main.go

@@ -0,0 +1,18 @@
+package main
+
+import "fmt"
+
+func main() {
+    var i interface{}
+    describe(i)
+
+    i = 42
+    describe(i)
+
+    i = "hello"
+    describe(i)
+}
+
+func describe(i interface{}) {
+    fmt.Printf("(%v, %T)\n", i, i)
+}