[Mono-bugs] [Bug 81277][Nor] New - Autoboxing an array of value types

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Changed by patperry at stanford.edu.

http://bugzilla.ximian.com/show_bug.cgi?id=81277

--- shadow/81277	2007-03-30 15:32:48.000000000 -0500
+++ shadow/81277.tmp.13223	2007-03-30 15:32:48.000000000 -0500
@@ -0,0 +1,105 @@
+Bug#: 81277
+Product: Mono: Compilers
+Version: 1.2
+OS: All
+OS Details: all platforms
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Normal
+Component: C#
+AssignedTo: rharinath at novell.com                            
+ReportedBy: patperry at stanford.edu               
+QAContact: mono-bugs at ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: Autoboxing an array of value types
+
+Description of Problem:
+
+I have a struct MyStruct that implements the IList<int> interface.  gmcs
+will not let me convert from MyStruct[] to IList<int>[].  I'm not sure if
+this makes sense or not-- the ECMA spec doesn't talk explicitly about
+autoboxing arrays of value types.  The microsoft compiler forbids this
+behavior.  I think this is probably the correct behavior.
+
+On the other hand, gmcs *will* let me convert from MyStruct[] to
+IList<IList<int>>.  However, after compiling the code, when it gets run
+with mono (or with the microsoft runtime), a System.NullReferenceException
+gets thrown with the message "Object reference not set to an instance of an
+object".  The microsoft compiler will not let me convert from MyStruct[] to
+IList<IList<int>>.
+
+I don't really know what the correct behavior is in the second case.  The
+ECMA spec doesn't explicitly forbid it, and it seems legal to me, but I
+could be wrong.
+
+Steps to reproduce the problem:
+
+1. Compile the code below:
+
+########## START ##############
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+public struct MyStruct : IList<int> {
+	public int this [int x] { get { return 0; } set { return; } }
+	public int IndexOf (int x) { return 0; }
+	public void Insert (int x, int y) { return; }
+	public void RemoveAt (int x) { return; }
+	public int Count { get { return 0; } }
+	public bool IsReadOnly { get { return false; } }
+	public void Add (int x) { return; }
+	public void Clear () { return; }
+	public bool Contains (int x) { return false; }
+	public void CopyTo (int[] x, int y) { return; }
+	public bool Remove (int x) { return false; }
+	public IEnumerator<int> GetEnumerator() { yield return 0; }
+	IEnumerator IEnumerable.GetEnumerator() { yield return 0; }
+}
+
+public class A  {
+
+    // This version does not compile:
+    public A(IList<int>[] x) { int y = x.Length; }
+
+    // This version compiles fine, but results in an exception:
+    public A(IList<IList<int>> x) { int y = x.Count; }
+
+}
+
+public class Test {
+	static void Main () {
+		MyStruct[] myStructArray = new MyStruct[1];
+
+        Console.WriteLine("Trying to construct an A...");
+		A a = new A(myStructArray);
+		Console.WriteLine("success!");
+	}
+}
+
+########## END ##############
+
+2. run with mono 
+
+Actual Results:
+
+Trying to construct an A...
+
+Unhandled Exception: System.NullReferenceException: Object reference not
+set to an instance of an object
+  at A..ctor (IList`1 x) [0x00000] 
+  at Test.Main () [0x00000] 
+
+
+Expected Results:
+
+Trying to construct an A...
+success!
+
+How often does this happen? 
+
+always