Changes between Initial Version and Version 1 of code/Singleton

Timestamp:

Feb 26, 2008, 6:38:37 PM (18 years ago)

Author:

landauf

Comment:

—

code/Singleton

@@ +1 @@
+= Singleton =
+
+== Description ==
+
+The [wiki:singleton] is an important design-pattern in advanced c++ coding. A singleton is a class, that allows only one existing instance at a time. This is achieved by overloading the constructor as a private function and the implementation of a static funciton that returns a pointer to the only existing instance (or creates the instance if it's not already existing). The pointer itself is stored in a static variable. This variable must be statically set to zero before you access the [wiki:singleton] the first time.
+
+This way you can retrieve a pointer to the [wiki:singleton] and access its member functions everywhere in the code without using ugly static objects or completely static classes.
+
+== Example ==
+
+{{{
+#!cpp
+class SlaveSingleton
+{
+  public:
+    static SlaveSingleton* getSingleton()
+    {
+      if (!pointer_s)
+        pointer_s = new SlaveSingleton();
+
+      return pointer_s;
+    }
+
+    void sendToWork()
+      { this->motivation_--; }
+
+    void bash()
+      { this->health_ -= 10; this->motivation_++; }
+
+    void feed()
+      { this->health_ += 5; }      
+
+  private:
+    SlaveSingleton() : health_(100), motivation_(0)
+      { std::cout << "The slave is born." << std::endl; }
+
+    SlaveSingleton* pointer_s;
+    int health_;
+    int motivation_;
+};
+
+SlaveSingleton* SlaveSingleton::pointer_s = 0;
+}}}
+
+{{{
+#!cpp
+SlaveSingleton::getSingleton()->bash();
+SlaveSingleton::getSingleton()->sendToWork();
+}}}