The IList interface requires an Add method. Arrays implement this function but it simply throws a NotImplementedException. This seems like very bad design to me.
What were the designers thinking when they did this?
+4
A:
ILists can be readonly - if in doubt the caller can test the IsFixedSize property before attempting to add or remove an element, or the IsReadOnly property before attempting to modify an element.
An array is a fixed-size IList.
It can be convenient to be able to treat an array as a list. One example is mocking a data access method that returns an IList - it can be mocked to simply return an array cast as an IList.
Joe
2009-09-08 20:19:26
It's actually the `IsFixedSize` property that you'd need to check. `IsReadOnly` will be `false` for arrays because the existing elements can be modified. `IsFixedSize` will be `true` because elements can't be added or removed.
LukeH
2009-09-08 21:26:28
Just to clarify the problem with fixed and read only: http://blogs.msdn.com/ericlippert/archive/2009/08/27/what-s-the-difference-between-fixed-and-fixed.aspx
Oliver
2009-09-09 07:02:49
@Oliver: I'm a big fan of Eric Lippert's blog, but that article has absolutely nothing to do with the `IsFixedSize` or `IsReadOnly` properties.
LukeH
2009-09-09 10:33:11