diff --git a/docs/errata/improvements.md b/docs/errata/improvements.md index f1f2775..fee6dfb 100644 --- a/docs/errata/improvements.md +++ b/docs/errata/improvements.md @@ -23,6 +23,7 @@ If you have suggestions for improvements, then please [raise an issue in this re - [Page 241 - Defining flight passengers](#page-241---defining-flight-passengers) - [Page 251 - Setting up a class library and console application](#page-251---setting-up-a-class-library-and-console-application) - [Page 254 - Calling methods using delegates](#page-254---calling-methods-using-delegates) +- [Page 265 - Implicit and explicit interface implementations](#page-265---implicit-and-explicit-interface-implementations) - [Page 270 - Equality of types](#page-270---equality-of-types) - [Page 299 - Treating warnings as errors](#page-299---treating-warnings-as-errors) - [Page 339 - Viewing source links with Visual Studio 2022](#page-339---viewing-source-links-with-visual-studio-2022) @@ -608,6 +609,94 @@ In the next edition, I will add a note to warn the reader either not to enter th delegate int DelegateWithMatchingSignature(string s); ``` +# Page 265 - Implicit and explicit interface implementations + +> Thanks to Rajiv S. for emailing with a question about this that caused me to think how to improve this section. + +In this section, I explain the difference between implicit and explicit interface implementations. + +I give an example of two interfaces, as shown in the following code: + +```cs +public interface IGamePlayer +{ + void Lose(); +} +public interface IKeyHolder +{ + void Lose(); +} +``` + +An improvement would be to point out that for interfaces, the default access modifier is `internal` and the default access modifier for interface members is `public` (instead of `private` which is the default for types like classes). + +In the examples above, both `Lose` methods must be `public` in any types that implement them. The members of an interface can only be `public` or `internal` unless they are given default implementations. + +In the next edition, I will add comments, as shown in the following code: + +```cs +public interface IGamePlayer // Defaults to internal. +{ + void Lose(); // Defaults to public. Could be internal. +} + +public interface IKeyHolder +{ + void Lose(); +} +``` + +Then I show a class that implements the two interfaces, as shown in the following code: + +```cs +public class Person : IGamePlayer, IKeyHolder +{ + public void Lose() // implicit implementation + { + // implement losing a key + } + + void IGamePlayer.Lose() // explicit implementation + { + // implement losing a game + } +} +``` + +To avoid conflicts with the `Person` class defined earlier in the chapter, in future editions I will change the class name to `Human`. I will also explain that any implicit implementations must be `public`, implement the methods by writing a suitable message to the console, and add comments too, as shown in the following code: + +```cs +public class Human : IGamePlayer, IKeyHolder +{ + // Implicit implementation must be public. + public void Lose() + { + WriteLine("Implementation for losing a key."); + } + + void IGamePlayer.Lose() // Explicit implementation can be private. + { + WriteLine("Implementation for losing a game."); + } +} +``` + +I will also update the code to show how to use the class, as shown in the following code: + +```cs +#region Calling implicit and explicit implementations + +Human human = new(); +human.Lose(); // Calls the implicit implementation i.e. losing a key. + +((IGamePlayer)human).Lose(); // Calls the explicit implementation. + +IGamePlayer player = human as IGamePlayer; +player.Lose(); // Calls explicit implementation of losing a game. + +#endregion +``` + # Page 270 - Equality of types > Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 17 March 2023](https://github.com/markjprice/cs11dotnet7/issues/44).