Merge branch 'template' of github.com:sensorario/go-design-patterns into template

Author: sensorario

behavioral/template/README.md

@@ -2,31 +2,64 @@
 
 ## Description
 
-Strategy pattern consists in different way to solve same problem. In Strategy
-entire algorithm is store in different classes. In Template pattern the
-algorithm is just one. The template define steps but some steps are deferred to
-user.
+Strategy pattern consists in a different way to solve same problem with
+different strategies. In Strategy entire algorithm is store in different
+classes. In Template pattern, instead, the algorithm is just one. The template
+defines steps but some other steps are deferred to user.
 
-This kind of pattern is widely used in MVC web frameworks when steps are always
-the same:
+## Implementation
 
- - Handle Request
- - Authentication
- - Authorization
- - Retrieve data from DB
- - Do something
- - Send Response
+In this case the template is a sort of flow of steps to solve a problem. While
+in strategy pattern each strategy implements entire solution, in this case the
+template define the steps execution but defer one or more steps to the user. In
+this case, the deferred step is called `templateSteps`.
 
-All these steps are execute for each http request. Just the `do something`
-part is defined by the user.
+```go
+type TheTemplate interface {
+	first() string
+	second() string
+	templateSteps(MessageRetriever) string
+}
+```
 
-## Implementation
+The `MessageRetriever` is an interface with `Message()` method. The template
+pattern here will joins strings. While first and third steps are implemented,
+the custom step is implemented by user.
+
+```go
+type MessageRetriever interface {
+	Message() string
+}
+```
+
+Now let's implement a concrete `Template`.
+
+```go
+type Template struct{}
+```
+
+In this case first and second steps are defined. The `templateSteps` will join
+different strings receiving the third step from outside.
+
+```go
+func (t *Template) first() string {
+	return "hello"
+}
+
+func (t *Template) second() string {
+	return "template"
+}
+```
 
 ```go
-type TranslatorRing interface {
-	Next(TranslatorRing)
-	GetNext() TranslatorRing
-	KnowsWord(s string) bool
-	TranslationOf(s string) string
+func (t *Template) templateSteps(m MessageRetriever) string {
+	return strings.Join(
+		[]string{
+			t.first(),
+			m.Message(),
+			t.second(),
+		},
+		" ",
+	)
 }
 ```