I’ve found myself in situations when I spent lots of time debugging because of some variables declared in a base class were written in tens or maybe hundreds of places in the whole hierarchy, across one or multiple projects even. How could you find the right place where the value of such a variable changes? Well, not easy unless you make some changes to the code. In this article I’m going to show how to create a small wrapper to help you there.<\/p>\n
But first, some rules of thumb:<\/p>\n
If you decide to go with the second rule that I mentioned I can bet you might be tempted to avoid the last advice and write it directly in the base class. Or if you won’t, one of your teammates will. To enforce that, you can use a wrapper class like the one show below.<\/p>\n
\r\ntemplate < typename T >\r\nclass ExplicitWriteVariable\r\n{\r\n\tT value_;\r\n\r\n\t\/\/ do not allow assigning values\r\n\tT& operator=(const T& val);\r\n\r\npublic:\r\n\tExplicitWriteVariable()\r\n\t{\r\n\t}\r\n\r\n\texplicit ExplicitWriteVariable(const T& val): value_(val)\r\n\t{\r\n\t}\r\n\r\n\tbool operator==(const ExplicitWriteVariable< T >& rhv)\r\n\t{\r\n\t\treturn value_ == rhv.value_;\r\n\t}\r\n\r\n\tbool operator!=(const ExplicitWriteVariable< T >& rhv)\r\n\t{\r\n\t\treturn value_ != rhv.value_;\r\n\t}\r\n\r\n\tbool operator==(const T& rhv)\r\n\t{\r\n\t\treturn value_ == rhv;\r\n\t}\r\n\r\n\tbool operator!=(const T& rhv)\r\n\t{\r\n\t\treturn value_ != rhv;\r\n\t}\r\n\r\n\t\/\/ allow assignment of the wrapper objects, and use Set for modifying the wrapper value\r\n\tExplicitWriteVariable< T >& operator=(const ExplicitWriteVariable< T >& rhv)\r\n\t{\r\n\t\tif(this != &rhv)\r\n\t\t{\r\n\t\t\tSet(rhv.value_);\r\n\t\t}\r\n\t\treturn *this;\r\n\t}\r\n\r\n\t\/\/ operator T is used for getting the wrapped value\r\n\toperator T () const\r\n\t{\r\n\t\treturn value_;\r\n\t}\r\n\r\n\t\/\/ this is the only entry point for setting the value of the variable\r\n\tvoid Set(const T& val)\r\n\t{\r\n\t\tvalue_ = val;\r\n\t}\r\n};\r\n\r\n<\/pre>\nThis template class has the following characteristics:<\/p>\n
If you use this to wrap variables in a base class you don’t make it private, but protected in the base class, otherwise you’ll have to provide get\/set accessors for the ExplicitWriteVariable object itself. The lacking of operator= will force you though to use the Set() method explicitly.<\/p>\n
Here are some samples for using the class:<\/p>\n
\r\nvoid Print(int val)\r\n{\r\n\tstd::cout << val << std::endl;\r\n}\r\n\r\nint main()\r\n{\r\n\tExplicitWriteVariable< int > val(10);\r\n\r\n\tPrint(val);\r\n\tif(val % 10 == 0) std::cout << \"multiple of 10\" << std::endl;\r\n\r\n\tval.Set(43);\r\n\r\n\tPrint(val);\r\n\tif(val % 2 == 1) std::cout << \"odd number\" << std::endl;\r\n\r\n\treturn 0;\r\n}<\/pre>\n\r\n10\r\nmultiple of 10\r\n43\r\nodd number\r\n<\/pre>\nThe following produces an error:<\/p>\n
\r\nExplicitWriteVariable< int > val(10);\r\nval = 43; \/\/ error C2248\r\n<\/pre>\n<\/p>\n","protected":false},"excerpt":{"rendered":"
I’ve found myself in situations when I spent lots of time debugging because of some variables declared in a base class were written in tens or maybe hundreds of places in the whole hierarchy, across one or multiple projects even. How could you find the right place where the value of such a variable changes? … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_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,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7],"tags":[104,451,105,106],"class_list":["post-242","post","type-post","status-publish","format-standard","hentry","category-c","tag-accessors","tag-c","tag-template","tag-wrapper"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t