feature: add PImpl Pattern demo code.

31.PImplPattern/02.Code/demo.cpp

@@ -0,0 +1,27 @@
+#include "demo.h"
+// include other necessary files
+#include ....
+
+class PAimpl
+{
+public:
+    void func1(int a, char* b) 
+    {
+        // implementation
+    }
+    bool isEnabled()
+    {
+        // implementation
+        return true;
+    }
+};
+
+void A::func1(int a, char* b)
+{
+    pimpl->func1(a, b);
+}
+
+bool A::isEnabled()
+{
+    return pimpl->isEnabled();
+}

31.PImplPattern/02.Code/demo.h

@@ -0,0 +1,22 @@
+/*  header file */
+
+// forward declaration
+class PAimpl;
+
+class A
+{
+public:
+    A()
+    {
+        // initial work
+    }
+    ~A() {
+        // free resource
+    }
+public:
+    void func1(int a, char* b);
+    bool isEnabled();
+    // other public interface which will exposed outside
+private:
+    PAimpl* pimpl;
+};