Differences

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--- programming:cpp-style-tips [2009/10/08 09:49]
cyril
+++ programming:cpp-style-tips [2013/09/19 16:41] (current)
@@ Line 248: / Line 248: @@
 ===== Copy of abstract objects =====
+==== Clone function ====
 You have an abstract class, and several implementations of this class. You have a pointer to the abstract class, but you don't know which implementations it is, and you want to make a copy of this object. The solution is to use a ''clone'' function.
@@ Line 258: / Line 260: @@
 };
-class Type1Descriptor
+class Type1Descriptor: public Descriptor
 {
  public:
   virtual Descriptor* clone()
   {
-    Type1Descriptor *result = new Type1Descriptor(*this);
+    return new Type1Descriptor(*this);
-    return result;
   }
 };
@@ Line 275: / Line 276: @@
   {
     my_descriptor = modelDescriptor->clone();
-    // I want a copy of the object, and not a reference, eg because I will customize it
   }
 };
 </code>
+==== Factory model ====
+If you just want to copy the configuration parameters of the class, you can create a Factory class that will have the same constructor parameters than your class and will store them internally, and that has a ''create'' function that will create a copy of the class with these parameters.
+<code cpp>
+class Descriptor
+{
+ public:
+  virtual void describe() = 0;
+  Descriptor(int param1, int param2): param1(param1), param2(param2) { internalData = 0; }
+};
+class DescriptorFactory
+{
+ public:
+  virtual Descriptor* create() const = 0;
+}
+class Type1Descriptor: public Descriptor
+{
+  int param1;
+  int param2;
+  int internalData;
+ public:
+  Descriptor(int param1, int param2): param1(param1), param2(param2) { internalData = 0; }
+  virtual void describe() { ... }
+};
+class Type1DescriptorFactory: public DescriptorFactory
+{
+  int param1;
+  int param2;
+ public:
+  Descriptor(int param1, int param2): param1(param1), param2(param2) {}
+  virtual Descriptor* create() const
+  {
+    return new Type1Descriptor(param1, param2);
+  }
+}
+class AnotherClass
+{
+  Descriptor *my_descriptor;
+ public:
+  AnotherClass(DescriptorFactory *descriptorFactory)
+  {
+    my_descriptor = descriptorFactory->create();
+  }
+};
+</code>
 ===== Inherited parameters =====