Question

Could you please suggest work around for .NET 4.0 defect which results into Common Language Runtime detected an invalid program. exception when following program is started (in Visual Studio 2010):

Note: Behavior does not reproduce when the same program is compiled in Visual Studion 2012.

namespace Namespace1
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;

    public class Tst1
    {
        public Action<DataType> Method1<DataType>(Func<DataType> param1) { return this.Method1<DataType>(param1, 0); }
        public Action<DataType> Method1<DataType>(Func<DataType> param1, int param2)
        {
            return param => System.Windows.Forms.MessageBox.Show(param1().ToString() + " " + param.ToString());
        }
    }

    public class TstBase { }

    public class Tst2 : TstBase { }

    public static class TstExtensions
    {
        public static string ExtensionMethod<TstType>(this TstType tst)
            where TstType : TstBase
        {
            return "From extension method";
        }
    }

    public class Application
    {
        public static void Main()
        {
            Tst1 tst1 = new Tst1();
            Tst2 tst2 = new Tst2();

            tst1.Method1<string>(tst2.ExtensionMethod)("From main");
        }
    }
}

Note: Assembly System.Windows.Forms.dll of .NET framework 4.0 needs to be referenced to build project.

Background information

I develop high-abstraction-level script-processing keyword-driven test automation framework upon low-level test automation tool shipped by 3-rd party (automation framework which performs keyword-driven scripts of high abstraction level with 3-rd party tool employed for accessing graphic UI on lower level). Construction listed above is required to implement uniform values validation approach.

Each element of listed code stand for following:

• Tst1 – class for validation of values
• Method1 – polymorphic method that performs validation of values which are being retrieved from UI (user interface) and can accept timeout to wait till UI element will acquire required value
• TstBase – base class for all UI controls handling from 3-rd party low-level automation tool API
• Tst2 – class for handling certain type of controls from 3-rd party low-level automation tool API
• ExtensionMethod – generic method for retrieving text from controls of all types using instance of any control-handler-class from 3-rd party low-level automation tool API

Method1 returns delegate which is passed as argument to other method that retrieves value from test-script-step parameters and immediately makes use of it. Altogether it looks like following:

testStepParameters.MakeUseOf("Field1ExpectedValue", validation.Verify<string>(field1.GetValue));

where validation.Verify<string>(field1.GetValue) goes instead of tst1.Method1<string>(tst2.ExtensionMethod) from first-most code snippet.

Important notice

I found one work-around for the defect but I do not like it because it adds some extent of clumsiness to the code. Work around that I found is to replace direct usage of extension method with Lambda expression – i.e. bug does no reproduce when line:

tst1.Method1<string>(tst2.ExtensionMethod)("From main");

is replaced with line:

tst1.Method1<string>(() => tst2.ExtensionMethod())("From main");

In final form it looks like:

testStepParameters.MakeUseOf("Field1ExpectedValue", validation.Verify<string>(() => field1.GetValue()));

And usage of that work-around becomes completely unpleasant when instead of field1 variable is used a complicated call for retrieving control (probably a delegate returning control – which is especially useful to check control state over time without bothering about how control is retrieved – with its own implementation of GetValue extension method).

Answer 1

You can fix it by creating the delegate yourself instead of letting C# do it for you. Like this:

 tst1.Method1<string>(new Func<string>(tst2.ExtensionMethod))("From main");