The method TypeAccessor.WriteSetter throws an ArgumentNullException, if the target type has a property with a non-public setter. (Line 141: http://code.google.com/p/fast-member/source/browse/FastMember/TypeAccessor.cs#141)

Example: class TestTarget { public int Id { get; private set; } }

I am not sure why prop.GetSetMethod() returns null, although prop.CanWrite obviously returned true in line 129.

Not sure if this is the best (fastest) way, but adding this at line 130 fixes this:

var setMethod = prop.GetSetMethod(); if (setMethod == null || !setMethod.IsPublic) continue;

http://code.google.com/p/fast-member/source/browse/FastMember/TypeAccessor.cs#130

Comment deleted

I think this line:

if (prop.GetIndexParameters().Length != 0 || !prop.CanWrite) continue;

should be:

if (prop.GetIndexParameters().Length != 0 || !prop.CanWrite || !prop.GetSetMethod().IsPublic) continue;

It seems the intention there is that CanWrite would return false if the property is not writeable, in fact all that CanWrite checks for is the existence of a set method, it does not however check the availability of that method.

I added a simple test that verifies this issue, and a fairly simple fix as well. I wasn't sure how to contribute (or if I could) code to this project, so I created a couple of diff files (using hg diff) and I've attached them here.