Today's C# quiz - does this compile?

 using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        IEnumerable<Inter1> ienum1 = new Class1[] { new Class1() };
        foreach (Class2 c in ienum1)
        {
            Console.WriteLine(c);
        }
    }
}

public interface Inter1 { }
public class Class1 : Inter1 { }
public class Class2 { }

Comments

• Anonymous
  November 16, 2007
  No, it won't compile. Class2 has no relation to Class1 or Inter1. c has to be either of type Class1 or Inter1 for this to compile.

• Anonymous
  November 16, 2007
  Why is this question so simple? I was expecting questions that only C# MVPs can solve.

• Anonymous
  November 16, 2007

csc temp.cs

Microsoft (R) Visual C# 2008 Compiler version 3.5.20921 for Microsoft (R) .NET Framework version 3.5 Copyright (C) Microsoft Corporation. All rights reserved.

temp

Unhandled Exception: System.InvalidCastException: Unable to cast object of type 'Class1' to type 'Class2'.   at Program.Main(String[] args) Bonus question - why does it compile?

• Anonymous
  November 16, 2007
  The comment has been removed

• Anonymous
  November 16, 2007
  The comment has been removed

• Anonymous
  November 16, 2007
  using System; using System.Collections.Generic; class Program { static void Main( string [] args) { IEnumerable<Inter1>

• Anonymous
  November 16, 2007
  The comment has been removed

• Anonymous
  November 19, 2007
  It compiles because the foreach generates an iterator over types of the interface Inter1 and since the Interface is empty the signature of Class2 matches the interface even though it does not actually implement it.

• Anonymous
  November 19, 2007
  Good try, but even if you add something to the interface and don't add it to Class2, the code still compiles - you can change the last 3 lines, for instance, to this and it still compiles. public interface Inter1 { int MyProperty { get; } } public class Class1 : Inter1 { public int MyProperty { get { return 0; } } } public class Class2 { }

• Anonymous
  November 21, 2007
         foreach (Class2 c in ienum1)        {            Console.WriteLine(c);        } is equivalent to in this case to: IEnumerator<Iter1> e = null; try {  e = ienum1.GetEnumerator();  while(e.MoveNext())  {    Class2 instance =  (Class2) e.Current;    Console.WriteLine(instance);  } } finally {  e.Dispose(); } foreach includes an explicit cast.

• Anonymous
  November 23, 2007
  Got a few good comments to the quiz post , but nobody that commented got it right. I went ahead and sent

• Anonymous
  November 23, 2007
  Got a few good comments to the quiz post , but nobody that commented got it right. I went ahead and sent