CDataProcessor<\/code>\u00a0is used to:<\/p>\n\n- Get data from a file.<\/li>\n
- Process the data.<\/li>\n
- Print the result.<\/li>\n<\/ul>\n
And the main method invokes the methods of this class.<\/p>\n
![](\"https:\/\/www.codeproject.com\/KB\/architecture\/LowCouplgHighCohesnCPP\/c1.PNG\")
<\/p>\n
Drawback of this solution<\/h2>\n\n- Low cohesion: The\u00a0
CDataProcessor<\/code>\u00a0class has many responsibilities, so we can\u2019t easily reuse the algorithm in other applications.<\/li>\n- High coupling: the processing is high coupled with the console and also with the data provider.<\/li>\n<\/ul>\n
Design refactoring<\/h2>\nHigh cohesion<\/h4>\n
To improve the cohesion, each responsibility must be assigned to a different class, so we need three classes:<\/p>\n
\nCFileProvider<\/code>: To get data from a file.<\/li>\nCDataProcessing<\/code>: To process data, and this class can use other classes to complete the processing, but to simplify the design, we consider that’s sufficient for our processing.<\/li>\nCResultReporting<\/code>: To report result to a file.<\/li>\n<\/ul>\nSo each class has its own responsibility. The advantages of this design are:<\/p>\n
\n- Easy to understand the classes.<\/li>\n
- Easy to maintain.<\/li>\n
- Easy to reuse the classes in other applications.<\/li>\n<\/ul>\n
Low coupling<\/h4>\n
What happens if data exists in a database rather than a file? In our last design, our application is high coupled with a file provider.<\/p>\n
To resolve this problem, we need an interface that provide methods to get data from anywhere, and for the case of the file, we need a class that implement this interface.<\/p>\n
For that, using\u00a0NVI<\/a>\u00a0can be good solution. This pattern is more useful than using only abstract classes because it’s possible to define a pre- and post-condition. It’s a useful object-oriented programming technique, particularly at development time. Pre- and post-conditions ensure that invariants of a class hierarchy (and in general, an abstraction) are not violated at designated points during execution of a program.<\/p>\nIn our case, we can add the\u00a0IDataProvider<\/code>\u00a0interface.<\/p>\n![](\"https:\/\/www.codeproject.com\/KB\/architecture\/LowCouplgHighCohesnCPP\/ClassDiagram1.png\")
<\/p>\n
And\u00a0CFileProvider<\/code>\u00a0inherits from\u00a0IDataProvider<\/code>\u00a0to implement\u00a0GetDataFromImpl<\/code>, and the same design can be used for\u00a0CDataProcessing<\/code>\u00a0and\u00a0CReportResult<\/code>.<\/p>\nHere\u2019s the new collaboration between the classes after refactoring:<\/p>\n
![](\"https:\/\/www.codeproject.com\/KB\/architecture\/LowCouplgHighCohesnCPP\/c2.PNG\")
<\/p>\n
Class factory<\/h4>\n
In the latest design, the creation of the concrete instances of\u00a0IDataProvider<\/code>,\u00a0IDataProcessing<\/code>, and\u00a0IReportResult<\/code>\u00a0are created by the main method. A better approach is to assign this responsibility to a factory class, so a logic to instantiate a family of instances needed is isolated.<\/p>\nController<\/h4>\n
The orchestration between all classes is implemented in the main method. It’s better to assign this responsibility to a Controller class, so we can use it in other applications.<\/p>\n
The controller needs three classes to interact with them, so the question is how do we bind instances to the controller.<\/p>\n
We can bind the instances using these two\u00a0approach:<\/p>\n
\n\n- Add a method named\u00a0\u00a0
BindInstances(IDataProviderPtr,IDataProcesingPtr,IReportResultPtr)<\/code>.<\/li>\n- Define the Controler as template and the controller will be instantiated like that:<\/li>\n<\/ul>\n<\/ul>\n
CController<CFileProvider,CDataProcessor,CConsoleReport><\/pre>\nThe difference between the two solutions is that for the first one, each Data Provider must inherit from\u00a0IDataProvider<\/code>, and for the second one,\u00a0CFileProvider<\/code>\u00a0only needs the method\u00a0GetData(Data&)<\/code>\u00a0even if it\u2019s inherited from another class than\u00a0IDataProvider<\/code>.<\/p>\nThere are many discussions between C++ gurus about using OOP or templates. Here’s a good\u00a0article<\/a>\u00a0about this tension between the two approaches.<\/p>\nHere\u2019s the new collaboration between the classes after the refactoring:<\/p>\n
![](\"https:\/\/www.codeproject.com\/KB\/architecture\/LowCouplgHighCohesnCPP\/c3.PNG\")
<\/p>\n
Benefits of the refactoring<\/h2>\n
After refactoring, this application became more flexible and we can use it for different scenarios:<\/p>\n
\n- Can get data from file, database, XML file, CSV file, \u2026<\/li>\n
- Can process with many classes not just one.<\/li>\n
- Can report to console, file, \u2026<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
Coupling is usually contrasted with cohesion. Low coupling often correlates with high cohesion, and vice versa. Low coupling is often a sign of a well-structured computer system and a good design, and when combined with high cohesion, supports the general goals of high readability and maintainability. The goal of this case study is to show … Continue reading “Two easy approaches to leverage your C++ OOP design skills.”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[32,13],"class_list":["post-296","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-code-quality","tag-cpp"],"_links":{"self":[{"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/posts\/296","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/comments?post=296"}],"version-history":[{"count":4,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/posts\/296\/revisions"}],"predecessor-version":[{"id":300,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/posts\/296\/revisions\/300"}],"wp:attachment":[{"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/media?parent=296"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/categories?post=296"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cppdepend.com\/blog\/wp-json\/wp\/v2\/tags?post=296"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}