surfmuggle surfmuggle - 1 month ago 31
C# Question

Using Extension methods in RoslynPad

I try to understand an extension method similar to this code

var p = new Person("Tim");
p.LastName = "Meier";

// reader.Get<bool>("IsDerivat");
var IsOlivia = p.Get<bool>("Olivia");


This is my code inside RoslynPad:

public static class PersonExtensions
{
public static T Get<T>(this Person person, string name)
{
return (T)person.NewFirstName(name);
}
}

public class Person
{
public Person(string firstName)
{
this.FirstName = firstName;
}

public string FirstName {get; private set;}
public string LastName {get; set;}

public object NewFirstName(string name)
{
this.FirstName = name;
return (object) this.FirstName;
}
}


But i get this error


error CS1109: Extension methods must be defined in a top level static
class; PersonExtensions is a nested class


I found this question extension-methods-must-be-defined-in-a-top-level-static-class- and the answers are good.

Adding a
namespace Foo
returns


error CS7021: Cannot declare namespace in script code


It seems that roslynpad adds stuff behind the scene.
So how can i make sure that my extension method is defined in a top-level static class?

Answer

RoslynPad uses Roslyn's script language syntax, which does not allow extension methods in classes (because the entire script is actually a class, and C# doesn't allow extensions in nested classes).

Currently, your only option (besides referencing a compiled assembly that contains the extension class using #r directives) is to place the extension as a top-level method in the script. For example:

public static T Get<T>(this Person person, string name)
{
    return (T)person.NewFirstName(name);
}

var p = new Person("Tim");   
p.LastName = "Meier"; 

var IsOlivia = p.Get<bool>("Olivia"); // works 

PS - I'm the author of RoslynPad.