add template pattern

Author: sensorario

README.md

@@ -9,6 +9,7 @@
  * [Chain of responsiblity](behavioral/chain) [:notebook:](https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern)
  * [Strategy](behavioral/strategy) [:notebook:](https://en.wikipedia.org/wiki/Strategy_pattern)
  * [Command](behavioral/command) [:notebook:](https://en.wikipedia.org/wiki/Command_pattern)
+ * [Template](behavioral/template) [:notebook:](https://en.wikipedia.org/wiki/Template_pattern)
 
 ## [Creational](creational)
 

behavioral/README.md

@@ -7,3 +7,4 @@ We are going to deal with behaviors instead of define structures or encapsulate
  * [Strategy](strategy) [:notebook:](https://en.wikipedia.org/wiki/Strategy_pattern)
  * [Chain of Responsibility](chain) [:notebook:](https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern)
  * [Command](command) [:notebook:](https://en.wikipedia.org/wiki/Command_pattern)
+ * [Template](template) [:notebook:](https://en.wikipedia.org/wiki/Template_pattern)

behavioral/template/README.md

@@ -0,0 +1,32 @@
+# Template
+
+## 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.
+
+This kind of pattern is widely used in MVC web frameworks when steps are always
+the same:
+
+ - Handle Request
+ - Authentication
+ - Authorization
+ - Retrieve data from DB
+ - Do something
+ - Send Response
+
+All these steps are execute for each http request. Just the `do something`
+part is defined by the user.
+
+## Implementation
+
+```go
+type TranslatorRing interface {
+	Next(TranslatorRing)
+	GetNext() TranslatorRing
+	KnowsWord(s string) bool
+	TranslationOf(s string) string
+}
+```

behavioral/template/template.go

@@ -0,0 +1,71 @@
+package template
+
+import "strings"
+
+type MessageRetriever interface {
+	Message() string
+}
+
+type TheTemplate interface {
+	first() string
+	second() string
+	customStep(MessageRetriever) string
+}
+
+type Template struct{}
+
+func (t *Template) first() string {
+	return "hello"
+}
+
+func (t *Template) second() string {
+	return "template"
+}
+
+func (t *Template) customStep(m MessageRetriever) string {
+	return strings.Join(
+		[]string{
+			t.first(),
+			m.Message(),
+			t.second(),
+		},
+		" ",
+	)
+}
+
+type Anonymous struct{}
+
+func (a *Anonymous) first() string {
+	return "hello"
+}
+
+func (a *Anonymous) second() string {
+	return "template"
+}
+
+func (a *Anonymous) customStep(f func() string) string {
+	return strings.Join(
+		[]string{
+			a.first(),
+			f(),
+			a.second(),
+		},
+		" ",
+	)
+}
+
+type Wrapper struct {
+	myFunc func() string
+}
+
+func (a *Wrapper) Message() string {
+	if a.myFunc != nil {
+		return a.myFunc()
+	}
+
+	return ""
+}
+
+func MessageRetrieverAdapter(f func() string) MessageRetriever {
+	return &Wrapper{myFunc: f}
+}

behavioral/template/template_test.go

@@ -0,0 +1,48 @@
+package template
+
+import (
+	"strings"
+	"testing"
+)
+
+type EmbedTemplate struct {
+	Template
+}
+
+func (m *EmbedTemplate) Message() string {
+	return "world"
+}
+
+func TestCustomStepIsCalled(t *testing.T) {
+	t.Run("Using interfaces", func(t *testing.T) {
+		s := &EmbedTemplate{}
+		res := s.customStep(s)
+		check(res, " world ", t)
+	})
+
+	t.Run("Define custom step via anonymous function", func(t *testing.T) {
+		m := new(Anonymous)
+		res := m.customStep(func() string {
+			return "world"
+		})
+		check(res, " world ", t)
+	})
+
+	t.Run("Using anonymous functions adapted to an interface", func(t *testing.T) {
+		customStepStep := MessageRetrieverAdapter(func() string {
+			return "world"
+		})
+		if customStepStep == nil {
+			t.Fatal("Can not continue with a nil custom step")
+		}
+		template := Template{}
+		res := template.customStep(customStepStep)
+		check(res, " world ", t)
+	})
+}
+
+func check(res string, expected string, t *testing.T) {
+	if !strings.Contains(res, expected) {
+		t.Errorf("Expected string '%s' was not found on returned string '%s'\n", expected, res)
+	}
+}