implemented proxy pattern

structural/proxy/proxy.go

@@ -0,0 +1,37 @@
+package proxy
+
+import "errors"
+
+type Human struct {
+	Gender string
+	Age    int
+}
+
+type Bar interface {
+	Welcome(Human) error
+}
+
+type OpenBar struct {
+	Visitors []Human
+}
+
+func (b *OpenBar) Welcome(h Human) error {
+	b.Visitors = append(b.Visitors, h)
+	return nil
+}
+
+type BarProxy struct {
+	bar Bar
+}
+
+func (b *BarProxy) Welcome(h Human) error {
+	if h.Gender == "female" && h.Age < 20 {
+		return errors.New("Females under 20 not allowed.")
+	}
+
+	if h.Gender == "male" && h.Age < 18 {
+		return errors.New("Males under 18 not allowed.")
+	}
+
+	return b.bar.Welcome(h)
+}