问题
I'm working with expressions and I need a method which receives an object of some type (currently unknown). Something like this:
public static void Foobar(object Meh) { }
What I need to is make this method return a Nullable<T> version of Meh, but the type T is from Meh.GetType(). So the return would be Nullable<MehType>, where MehType is the type of Meh.
Any ideas or suggestions?
Thanks
Update: the reason why I needed this is because of this exception:
The binary operator Equal is not defined for the types 'System.Nullable`1[System.Int32]' and 'System.Int32'.
return Expression.Equal(leftExpr, rightExpr);
where leftExpr is a System.Nullable1[[System.Int32 and rightExpr is a System.Int32.
回答1:
If you don't know the type at compile time, the only way of expressing it is as object - and as soon as you box a nullable value type, you end up with either a null reference, or a boxed non-nullable value type.
So these snippets are exactly equivalent in terms of the results:
int? nullable = 3;
object result = nullable;
int nonNullable = 3;
object result = nonNullable;
In other words, I don't think you can really express what you're trying to do.
回答2:
Do you have to use Meh.GetType() instead of a generic? What about this?
public static Nullable<T> Foobar<T>(T Meh) where T : struct { }
I'm making the assumption that "some type" does not mean "any type", because the solution above would only work with value types.
来源：https://stackoverflow.com/questions/7070791/how-to-create-a-nullablet-from-a-type-variable