{"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":"<p>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<p>However, if you have member variables that are involved in any kind of dynamic allocations, you&#8217;re going to need to override the default copy\/assignment functions with your own &#8220;deep copy&#8221; versions.\u00c2\u00a0 <!--more-->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&#8217;s an all-or-nothing affair &#8211; 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 &#8211; it flies in the face of the most basic maintenance-friendly design philosophy: encapsulate similar functionality in one place.<\/p>\n<p>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 <strong>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<p>I suggest the following strategy when the above criteria are met:<\/p>\n<ul>\n<li>for original class foo, split into&#8230;<\/li>\n<ul>\n<li>foo_shallow &#8211; a base class that uses the built-in shallow copy\/assignment functions; the ONLY purpose of this class is to provide those built-in functions, and there should be nothing in it but simple member variables<\/li>\n<li>foo &#8211; a derived class with deep copy copy\/assignment functions; these functions call the built-in base class versions<\/li>\n<\/ul>\n<li>all of the functionality can stay in foo, where all variables are available<\/li>\n<\/ul>\n<p>Fun fun, party on!<\/p>\n","protected":false},"excerpt":{"rendered":"<p>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. However, if you have member variables that are involved in [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"enabled":false},"version":2}},"categories":[10],"tags":[106],"class_list":["post-129","post","type-post","status-publish","format-standard","hentry","category-tricks-tips-tools","tag-design"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9M11L-25","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/posts\/129","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/comments?post=129"}],"version-history":[{"count":1,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/posts\/129\/revisions"}],"predecessor-version":[{"id":1181,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/posts\/129\/revisions\/1181"}],"wp:attachment":[{"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/media?parent=129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/categories?post=129"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bitpost.com\/news\/wp-json\/wp\/v2\/tags?post=129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}