Generic method to type casting

Question

I'm trying to write generic method to cast types. I want write something like Cast.To<Type>(variable) instead of (Type) variable. My wrong version of this method:

public class Cast {     public static T To<T>(object o)     {         return (T) o;     } } 

And this is simple test:

public class A {     public static explicit operator B(A a)     {         return new B();     } }  public class B { }  A a = new A(); B b = Cast.To<B>(a); 

As you guessed, this code will fail with InvalidCastException.

Is this code fail because virtual machine doesn't know how to cast variable of type object to type B at run-time? But exception message says: "unable to cast object of type A to type B". So CLR knows about real type of variable o, why it cannot perform casting?

And here is main question: how should I rewrite method T To<T>(object o) to fix this problem?

Answer 1

All of what's been said about the operator resolution is correct...but this is my answer to your main question:

    public static T To<T>(this object o)     {         return (T)(dynamic)o;     } 

The key here is that casting o to dynamic will force the .NET to search for the explicit operator at runtime.

Plus, why not make it an extension method?

Instead of

        A a = new A();         B b = Cast.To<B>(a); 

you can do

        A a = new A();         B b = a.To<B>(); 

An added benefit of exposing it as an extension method is that you gain a fluent interface for explicit casting (if you like that sort of thing). I've always hated the amount of nested parenthesis balancing required for explicit casting in .NET.

So you can do:

a.To<B>().DoSomething().To<C>().DoSomethingElse()  

instead of

((C)((B)a).DoSomething())).DoSomethingElse() 

which, to me, looks clearer.