{"id":129,"date":"2006-05-31T20:35:59","date_gmt":"2006-06-01T01:35:59","guid":{"rendered":"http:\/\/bitpost.com\/news\/2006\/05\/31\/how-to-design-maintainable-c-objects\/"},"modified":"2011-04-06T19:31:51","modified_gmt":"2011-04-07T00:31:51","slug":"how-to-design-maintainable-c-objects","status":"publish","type":"post","link":"https:\/\/bitpost.com\/news\/2006\/how-to-design-maintainable-c-objects\/","title":{"rendered":"How to design maintainable C++ objects"},"content":{"rendered":"

A great feature of C++ is that shallow copy constructors and assignment operators are done for you. If you have a class with simple types, you automatically get the ability to construct a clone of any existing object, or assign any one object to another.<\/p>\n

However, if you have member variables that are involved in any kind of dynamic allocations, you’re going to need to override the default copy\/assignment functions with your own “deep copy” versions.\u00c2\u00a0 This leads me to the characteristic I find most annoying about C++: if you decide to write your own copy constructor or assignment operator, it’s an all-or-nothing affair – you lose the default version when you create your own. There can only be one, after all. But this means that if you have a class with dozens of constantly changing member variables, you have a real maintenance headache keeping the copy constructor and assignment operator up to date. You should use a common function for them (or call one from the other), but you still have to maintain the member variables in that function. This stinks – it flies in the face of the most basic maintenance-friendly design philosophy: encapsulate similar functionality in one place.<\/p>\n

The solution is two split the class into two subclasses. At first this sounds severe, and perhaps it is in a class with only a handful of member variables. But I propose that it is essential<\/strong> in the situation where you are dealing with a class that has both a large number of simple member variables alongside any dynamically allocated members requiring deep copying.<\/p>\n

I suggest the following strategy when the above criteria are met:<\/p>\n