implemented adapter pattern

structural/adapter/adapter.go

@@ -0,0 +1,51 @@
+package adapter
+
+//old bad service which we can't chane
+type OldEmailSender interface {
+	Send(from, to, subject, body string) error
+}
+
+type OldEmailSvc struct{}
+
+func (s OldEmailSvc) Send(from, to, subject, body string) error {
+	//Send email...
+	return nil
+}
+
+//new service ehich has state
+//we have client only supports this interface
+type NewEmailSender interface {
+	Send() error
+}
+
+type NewEmailService struct {
+	From, To, Subject, Body string
+}
+
+func (s NewEmailService) Send() error {
+	//state already initialized just send
+	return nil
+}
+
+//adapter for old email service
+type OldEmailServiceAdapter struct {
+	From, To, Subject, Body string
+	OldEmailService         OldEmailSender
+}
+
+func (a OldEmailServiceAdapter) Send() error {
+	return a.OldEmailService.Send(a.From, a.To, a.Subject, a.Body)
+}
+
+/*
+    client which only supports new email service interface
+	EmailClient{ Mail: OldEmailServiceAdapter{...}} old service
+	EmailClient{ Mail: NewEmailService{...}} new service
+*/
+type EmailClient struct {
+	Mail NewEmailSender
+}
+
+func (e EmailClient) SendEmail(From, To, Subject, Body string) error {
+	return e.Mail.Send()
+}