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c#.netclr

Did I instantiate an object of void?

As you all know, in C# we could not do something like this:

var voidObject = new void();

or

var voidObject = new System.Void();

or

var voidObject = Activator.CreateInstance(typeof(void));

But this code compiles successfully and in debug mode I can see that type of the voidObject is System.Void:

var voidObject = FormatterServices.GetUninitializedObject(typeof(void));

What is this? Is this real instance of void?

Solution

  • From what I can see it is a perfectly good, perfectly valid boxed System.Void value type :-)

    You can

    Console.WriteLine(voidObject.GetType());

    and see that it is a System.Void.

    System.Void is a value type, so creating it through FormatterServices.GetUninitializedObject should be equal to doing (object)default(void) (because FormatterServices.GetUninitializedObject will return a value type with all its fields set to their default value) (note that clearly (object)default(void) is illegal).

    Still there are not many things you can do with your boxed System.Void...

    var voidObject = System.Runtime.Serialization.FormatterServices.GetUninitializedObject(typeof(void));
var voidObject2 = System.Runtime.Serialization.FormatterServices.GetUninitializedObject(typeof(void));

Console.WriteLine("Type: {0}", voidObject.GetType());
Console.WriteLine("IsValueType: {0}", voidObject.GetType().IsValueType);

Console.WriteLine("Equals: {0}", voidObject.Equals(voidObject2));
Console.WriteLine("GetHashCode1: {0}", voidObject.GetHashCode());
Console.WriteLine("GetHashCode2: {0}", voidObject2.GetHashCode());
Console.WriteLine("ToString: {0}", voidObject.ToString());

    There seems to be some differences between .NET and Mono implementations... On .NET all the instances of System.Void have the same GetHashCode(), while on Mono every one of them has a different GetHashCode(). The Equals works correctly (true) for both of them.

    (note that the difference in the GetHashCode() seems to be a bug of Mono with structs without fields: https://ideone.com/t0t8I6 that should be fixed in newer releases)