Conversion from Func<object,string> to Func<string,string> works but to Func<int,string> fails
c#, contravariance, covariance, func, generics
Solution
It is because `Func` is defined as `Func<in T, out TResult>`, MSDN is here, so `T` is contra-variant with `in` keyword, that is, you can use either the type you specified or any type that is less derived, but remember that co-variance and contra-variance do not support for value type:
Why covariance and contravariance do not support value type
So, it works for `string` but does not work out with `int`. You might need to read more about covariance and contravariance:
http://msdn.microsoft.com/en-us/library/dd233060.aspx
http://msdn.microsoft.com/en-us/library/dd799517.aspx
Problem
I have the following code: ``` static Func<object, string> s_objToString = (x) => x.ToString(); static Func<string, string> s_stringToString = s_objToString; //compiles static Func<int, string> s_intToString = s_objToString; //error ``` The second line compiles but the third line fails to compile with error: Cannot implicitly convert type '`System.Func<object,string>`' to '`System.Func<int,string>`' Why is that? I understand that with genetics although string is derived from object a `List<string>` does not derive from `List<object>`, but here `object` to `string` works and `object` to `int` fails, why? OK let's say I understood why; the question now is there a way around it (other then defining `MyInt` class to box `int` because `Func<object,string>` to `Func<MyInt,string>` works)?