I think this is useful information for beginning C programmers. The reasons for a software developer not being able to change the original source code can be numerous. For example, the source class is part of a commercial package that you do not have the source code for.
Or there can be a licensing issue that prohibits a developer from changing the code. Whatever the reason for this hindrance is, it's clear that techniques like adding the methods to the original class or making it eat an interface are not possible options. So a developer needs to do something else. Exception objects for specific error handling functionality. These types of use-cases are limited only by your imagination and good sense. Extending predefined types can be difficult with struct types because they're passed by value to methods.
That means any changes to the struct are made to a copy of the struct. Those changes aren't visible once the extension method exits. Beginning with C 7. Adding the ref modifier means the first argument is passed by reference. This enables you to write extension methods that change the state of the struct being extended. While it's still considered preferable to add functionality by modifying an object's code or deriving a new type whenever it's reasonable and possible to do so, extension methods have become a crucial option for creating reusable functionality throughout the.
NET ecosystem. For those occasions when the original source isn't under your control, when a derived object is inappropriate or impossible, or when the functionality shouldn't be exposed beyond its applicable scope, Extension methods are an excellent choice. For more information on derived types, see Inheritance. When using an extension method to extend a type whose source code you aren't in control of, you run the risk that a change in the implementation of the type will cause your extension method to break.
For a class library that you implemented, you shouldn't use extension methods to avoid incrementing the version number of an assembly. If you want to add significant functionality to a library for which you own the source code, follow the. NET guidelines for assembly versioning. For more information, see Assembly Versioning. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy.
Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Extension methods cannot be used to override existing methods. The concept of extension methods cannot be applied to fields, properties or events. Overuse of extension methods is not a good style of programming. Conclusion I hope this article will help you to understand Extension Methods in C 3.
C extension methods extension method. Next Recommended Reading. Windows 10 Vs Windows Visual Studio Vs Visual Studio Understanding Matplotlib With Examples. Understanding Numpy With Examples. C Evolution. Everything That Every. How to extend a Class in C? Asked 8 years, 8 months ago. Active 3 years, 9 months ago. Viewed k times. Improve this question. Show us Person class.. Please show the definition of class Person.
I can't! It is not "Person" in fact, it's another class in a DLL, but this shouldn't important? I believe you meant to explicitly cast straight to Student — Basic. A Student is a Person but the opposite is not necessarily true - a Person is not always a Student. That is why your cast is failing. Add a comment. Active Oldest Votes. You cannot convert a Person to Student directly. You cannot cast base class to derived class One possible solution is : Create Student from Person using constructor overload.
0コメント