Checking if a type is void

[Stefan Koch]

Good Day everyone, I know it has been a while since I last posted 
on here.

Did you know that you could check if a type is void without 
having to mention the type void?

And you do it like this

```D
template isVoid(alias X)
{
     enum bool isVoid = is(mixin(`!X`));
}

pragma(msg, isVoid!(int));
```
Check it out for yourself ;)


The reason this is that internally a TypeExpression is created 
and all Expressions defined a `!` operation.
Because all of them are values/ do have init-expressions.

Except for the one type that doesn't which is void.

Which is why you cannot create an init expression for void, and 
that makes the expression `!void` fail during the semantic checks.

Cheers,

Stefan