diff --git a/docs/errata/improvements.md b/docs/errata/improvements.md index add7180..ee199cf 100644 --- a/docs/errata/improvements.md +++ b/docs/errata/improvements.md @@ -19,6 +19,7 @@ If you have suggestions for improvements, then please [raise an issue in this re - [Page 237 - Implementing functionality using methods](#page-237---implementing-functionality-using-methods) - [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 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) @@ -466,6 +467,38 @@ message saying that required assets are missing, click Yes to add them. Harry was born on a Sunday. ``` +# Page 254 - Calling methods using delegates + +> Thanks to `Jovis#7721` in the Discord channel for raising this issue. + +This section shows example code that defines a method and a matching delegate. This code is not meant to be entered into your existing project. The reason is because you cannot just declare a type (like a class, or a delegate as in this example) in the middle of a top-level program. + +A delegate declaration, as shown in the following code: +```cs +delegate int DelegateWithMatchingSignature(string s); +``` + +Will give the following compile error: +``` +CS8803: Top-level statements must precede namespace and type declarations. +``` + +If you try to enter it along with the following code in `Program.cs`: + +```cs +// create a delegate instance that points to the method +DelegateWithMatchingSignature d = new(p1.MethodIWantToCall); + +// call the delegate, who then calls the method +int answer2 = d("Frog"); +``` + +In the next edition, I will add a note to warn the reader either not to enter this code, or to tell them to put the in a separate file, as shown in the following code: +```cs +// In a separate file like Program.Delegates.cs. +delegate int DelegateWithMatchingSignature(string s); +``` + # 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).