Question

  public static class Helper
  {
    public static float ToFloat(this string input)
    {
      float result;
      return float.TryParse(input, out result) ? result : 0;
    }
  }

I have added the following at top:

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(AttributeTargets.Method)]
    public class ExtensionAttribute : Attribute
    {
        public ExtensionAttribute()
        {

        }
    }
}

But still I get Type expected error on “this” in Helper class. What’s the problem ?

Answer 1

Weird, the following compiles and runs fine when targeting .NET 2.0:

using System;

namespace System.Runtime.CompilerServices
{
    [AttributeUsage(AttributeTargets.Method)]
    public class ExtensionAttribute : Attribute
    {
        public ExtensionAttribute()
        {

        }
    }
}

public static class Helper
{
    public static float ToFloat(this string input)
    {
        float result;
        return float.TryParse(input, out result) ? result : 0;
    }
}

class Program
{
    static void Main()
    {
        string foo = "123";
        Console.WriteLine(foo.ToFloat());
    }
}