Union Support like c++ Union

[andrevdl]

It would be great if c# supports Union.

Yes, you can create a struct with all types, like:

struct Example {
	int a;
	float b;
	...
}

And then do manual magic with struct layout Kind.
But this will only work for fix size elements and you must know the sizes of the objects.

[bondsbw]

Dupe of #687. See also #399.