If you've ever used reflection, you might have noticed that the return type of a void method is not simply null. Instead, it is System.Void.
Sure, whatever, just a placeholder so that Type.ReturnType never returns null, right?
System.Void is an empty struct. No methods, no properties, no fields, no attributes, no nothing.
So, just for fun, can we create an object of type System.Void, so that voidObject.GetType() == typeof(void) is true? I mean, it's just an empty struct, how hard can it be?
TL;DR: No.
First of all, System.Void doesn't show up in IntelliSense. It's hidden from being recommended. Off to a good start.
Next, let's just use the new keyword. new System.Void();, how hard can it be? Well, you see, System.Void is illegal C# syntax. You cannot even reference this type directly, as doing so will result in a CS0673 diagnostics error. Yes, there's literally a unique diagnostics error specifically for referencing this particular type. I'm starting to suspect this is more than just a placeholder type used for reflection.
Alright, CS0673 tells us to use typeof(void), so how about using Activator.CreateInstance? You give it a type, and it attempts to create a new instance of that type. Heh, no. NotSupportedException.
Hmm, okay. Anyone who has skimmed through the .NET source code has probably come across references to RuntimeHelpers. Maybe that will help me on my quest? Hah, no, fat chance. Using it with typeof(void) throws an ArgumentException. Another dead end.
Fine. What if we create our own memberless struct, and use reflection to create a delegate of Unsafe.As which converts from FakeVoid to System.Void? Nope, System.Void cannot be used as a generic argument. So anything that relies on generics is going to fail if one of the arguments is System.Void, even if that method is internal to the .NET runtime itself. Well, shit.
Okay, what if we create a type at runtime, and define a field on that type which has the type System.Void? Nope, TypeBuilder.DefineField throws an ArgumentException if the field type is System.Void.
Alright, now the gloves are coming off! How about using DynamicMethod and ILGenerator to create a method at runtime which returns default(System.Void)? Nope, InvalidProgramException.
Time to pull out the big guns. What if we use DynamicMethod to generate a method at runtime which replicates unsafe code that casts a FakeVoid* to a Void*? Nope, same error as the above. Using pointer didn't make any difference whatsoever.
Alas, I have reached my wits' end. I have no more ideas or tricks up my sleeves. The compiler and runtime actively refuses any and all attempt at creating an instance of System.Void.
Sadly, the clever people of the .NET team seem to have done their homework on this one. Surely, this is because System.Void isn't just a placeholder, but actually the type that the runtime uses internally to represent void? Right?
<see cref="Void"/> in XML comments appear as if they're references to void in Visual Studio's hover-over tooltip. Is this a hint of what is actually happening, or am I just being paranoid?
Regardless, I admit defeat. I have, quite literally, failed to create nothing.