System.NullReferenceException: Object reference not set to an instance of an object.

[donaldnevermore]

OS: Windows 10
dotnet version: 5.0.400

Step to reproduce: run the sample code.

using System;
using CSScriptLib;

var calc = CSScript.Evaluator
    .LoadCode<ICalc>(@"using System;
                                    public class Script
                                    {
                                        public int Sum(int a, int b)
                                        {
                                            return a+b;
                                        }
                                    }");
var result = calc.Sum(1, 2);
Console.WriteLine(result);

public interface ICalc {
    int Sum(int a, int b);
}

Output:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at CSScriptLib.EvaluatorBase`1.LoadCode[T](String scriptText, Object[] args)
   at <Program>$.<Main>$(String[] args) in E:\Monorepos\test-driven-design\Main.cs:line 4

[oleg-shilo]

Hi Donald,

There is a critical mistake in the API documentation. It states that LoadCode<T> returns aligned to interface object (duck-typed):

This is true only for the LoadMethod<T> but not for LoadCode<T> returns a canonical typecasted object. This is due to the fact that LoadMethod decorates it with the class definition so it can inject inheritance statement but LoadCode processes the code as-is and cannot inject anything.

You can fix your code by moving to LoadMethod:

var calc = CSScript.Evaluator
                   .LoadMethod<ICalc>(@"using System;
                                        public int Sum(int a, int b)
                                        {
                                            return a+b;
                                        }");
var result = calc.Sum(1, 2);
Console.WriteLine(result);

or explicitly implementing the interface:

var calc = CSScript.Evaluator
                   .LoadCode<ICalc>(@"using System;
                                      public class Script : ICalc
                                      {
                                          public int Sum(int a, int b)
                                          {
                                              return a+b;
                                          }
                                      }");
var result = calc.Sum(1, 2);
Console.WriteLine(result);

[oleg-shilo]

The documentation is fixed now and will be available with the very next release