syntax question on "invariant" keyword

[Michael Kiermaier]

I tried an example from
http://www.digitalmars.com/d/final-const-invariant.html:

*** begin Test.d ***
import std.stdio;

struct S
{
    int x;
    invariant int y;
}

void main() {
    writefln(S.sizeof); // prints 4, not 8
}
*** end Test.d ***

Compilation gives the error message
Test.d(5): statement expected to be { }, not int

So I changed the line
    invariant int y;
into
    invariant {int y;}
and now the compilation works.


Why do I need the curly braces here?
And why does the example not work? Was there a change to the syntax rules of "invariant"?

Tanks in advance,

~michael