Reflection on structure differs from class - but only in code

Question

Code snippet:

Dim target As Object
\' target gets properly set to something of the desired type
Dim field As FieldInfo = target.GetType.GetField(\"fieldName\         


        

Answer 1

Working with your original sample, I agree that it works in C# but not in VB! If you use Reflector or ILDasm you will see that the call to Field.SetValue(target, ...) is actually compiled (in VB) as:

field.SetValue(RuntimeHelpers.GetObjectValue(target), ...)

GetObjectValue "Returns a boxed copy of obj if it is a value class; otherwise obj itself is returned." I.e. the value is being set on a copy of your struct!

This link gives the explanation (such as it is). The workaround is to declare target as System.ValueType instead of Object. I'm not sure if that actually helps in your real-life code: you may need a messy type test to be able to handle value types separately from reference types.