typeof(Array).GetInterfaces() changes behaviour in .NET 2.0

When we migrated an existing project from .NET 1.1 to .NET 2.0 Gerhard (who owns http://www.objectmapper.net/) noted that his mapper suddenly had problems. The cause was an interesting change in the CLR/CTS:

Suppose you were using the interfaces an array exposes like that:

int[] arrayOfInt = new int[]{1,4,5}; Type[] interfaces = arrayOfInt.GetType().GetInterfaces(); int i = interfaces.Length; // number of supported interfacesobject o = arrayOfInt; int b = 0; // counter for implemented interfaces if (o is ICollection)   ++b; if (o is IList)     ++b; if (o is IEnumerable)     ++b;

In .NET 1.1 the resulting value of i was 0. No interfaces supported by arrays, sorry. No, wait! b was 3! So it supports interfaces, but it doesn’t tell!

One may be inclined to call this a bug…. 😉

Anyway, run the same code in .NET 2.0 and the result of i is 7. The interfaces returned are:

• {Name = “ICloneable” FullName = “System.ICloneable”}
• {Name = “IList” FullName = “System.Collections.IList”}
• {Name = “ICollection” FullName = “System.Collections.ICollection”}
• {Name = “IEnumerable” FullName = “System.Collections.IEnumerable”}
• {Name = “IList`1” FullName = “System.Collections.Generic.IList`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]”}
• {Name = “ICollection`1” FullName = “System.Collections.Generic.ICollection`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]”}
• {Name = “IEnumerable`1” FullName = “System.Collections.Generic.IEnumerable`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]”} 

Noteworthy that it implements the old non-generic collection interfaces as well as the new generic ones.

That’s all for now folks,
AJ.NET

Advertisement