From 3d2d78a8a2e2ab3081c9b378a64b9847774c3623 Mon Sep 17 00:00:00 2001
From: Tamer Tas <contact@tmrts.com>
Date: Sat, 14 May 2016 16:12:50 +0300
Subject: [PATCH] Add singleton creational pattern

---
 README.md               |  4 ++--
 creational/singleton.md | 35 +++++++++++++++++++++++++++++++++++
 singleton/singleton.go  | 20 --------------------
 3 files changed, 37 insertions(+), 22 deletions(-)
 create mode 100644 creational/singleton.md
 delete mode 100644 singleton/singleton.go

diff --git a/README.md b/README.md
index 00448df..8b694da 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ __Creational Patterns__:
 | [Builder](builder/builder.go) | Builds a complex object using simple objects |
 | [Factory Method](factory_method.go) | Defers instantiation of an object to a specialized function for creating instances |
 | [Object Pool](object_pool/pool.go) | Instantiates and maintains a group of objects instances of the same type |
-| [Singleton](singleton/singleton.go) | Restricts instantiation of a class to one object |
+| [Singleton](creational/singleton.md) | Restricts instantiation of a type to one object |
 
 __Structural Patterns__:
 
@@ -29,7 +29,7 @@ __Structural Patterns__:
 | [Bridge](bridge.go) | Decouples an interface from its implementation so that the two can vary independently |
 | [Composite](composite.go) | Encapsulates and provides access to a number of different objects |
 | [Decorator](structural/decorator.md) | Adds behavior to an object, statically or dynamically |
-| [Facade](facade.go) | Uses one class as an API to a number of others |
+| [Facade](facade.go) | Uses one type as an API to a number of others |
 | [Flyweight](flyweight.go) | Reuses existing instances of objects with similar/identical state to minimize resource usage |
 | [Model View Controller](mvc.go) | Divides an app into three interconnected parts to separate internal representation from presentation to user |
 | [Proxy](proxy.go) | Provides a surrogate for an object to control it's actions |
diff --git a/creational/singleton.md b/creational/singleton.md
new file mode 100644
index 0000000..0c0c54d
--- /dev/null
+++ b/creational/singleton.md
@@ -0,0 +1,35 @@
+#Singleton Pattern
+Singleton creational design pattern restricts the instantiation of a type to a single object.
+
+## Implementation
+```go
+package singleton
+
+type singleton map[string]string
+
+var once sync.Once
+
+var instance *singleton
+
+func New() *singleton {
+	once.Do(func() {
+		instance = make(singleton)
+	})
+
+	return instance
+}
+```
+
+## Usage
+```go
+s := singleton.New()
+
+s["this"] = "that"
+
+s2 := singleton.New()
+
+// s2["this"] == "that"
+```
+
+## Rules of Thumb
+- Singleton pattern represents a global state and most of the time reduces testability.
diff --git a/singleton/singleton.go b/singleton/singleton.go
deleted file mode 100644
index d85a4a6..0000000
--- a/singleton/singleton.go
+++ /dev/null
@@ -1,20 +0,0 @@
-package singleton
-
-import (
-	"sync"
-)
-
-type Object struct {
-}
-
-var once sync.Once
-var instance *Object
-
-func GetInstance() *Object {
-	// Creates a singleton instance once.
-	once.Do(func() {
-		instance = &singleton{}
-	})
-
-	return instance
-}