SharedTypes: add comment why we don't void,int, etc.

ICSharpCode.NRefactory/TypeSystem/IType.cs

@@ -23,6 +23,9 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		/// <summary>
 		/// Gets the element type of array or pointer types.
 		/// </summary>
+		/// <exception cref="InvalidOperationException">
+		/// This type is not an array or pointer type.
+		/// </exception>
 		IType GetElementType();
 		
 		/// <summary>

ICSharpCode.NRefactory/TypeSystem/Implementation/DefaultTypeDefinition.cs

@@ -386,10 +386,15 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 			if (other == null)
 				return false;
 			if (declaringTypeDefinition != null) {
-				return declaringTypeDefinition.Equals(other.DeclaringTypeDefinition) && this.Name == other.Name && this.TypeParameterCount == other.TypeParameterCount;
+				return declaringTypeDefinition.Equals(other.DeclaringTypeDefinition)
+					&& this.Name == other.Name
+					&& this.TypeParameterCount == other.TypeParameterCount;
 			} else {
-				return other.DeclaringTypeDefinition == null && this.ProjectContent == other.ProjectContent
-					&& this.Namespace == other.Namespace && this.Name == other.Name && this.TypeParameterCount == other.TypeParameterCount;
+				return other.DeclaringTypeDefinition == null 
+					&& this.ProjectContent == other.ProjectContent
+					&& this.Namespace == other.Namespace 
+					&& this.Name == other.Name 
+					&& this.TypeParameterCount == other.TypeParameterCount;
 			}
 		}
 		

ICSharpCode.NRefactory/TypeSystem/SharedTypes.cs

@@ -22,5 +22,23 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		/// </summary>
 		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2104:DoNotDeclareReadOnlyMutableReferenceTypes", Justification = "It's immutable")]
 		public readonly static IType Null = new NullType();
+		
+		/*
+		 * I'd like to define static instances for common types like
+		 * void, int, etc.; but there are two problems with this:
+		 * 
+		 * SharedTypes.Void.GetDefinition().ProjectContent should return mscorlib, but
+		 * we can't do that without providing a context.
+		 * Assuming we add a context parameter to GetDefinition():
+		 * 
+		 * SharedType.Void.Equals(SharedType.Void.GetDefinition(x))
+		 * SharedType.Void.GetDefinition(y).Equals(SharedType.Void)
+		 * should both return true.
+		 * But if the type can have multiple definitions (multiple mscorlib versions loaded),
+		 * then this is not possible without violating transitivity of Equals():
+		 * 
+		 * SharedType.Void.GetDefinition(x).Equals(SharedType.Void.GetDefinition(y))
+		 * would have to return true even though these are two distinct definitions.
+		 */
 	}
 }