Created attachment 151505 [details]
The source code that generated the error.

The constructor of a class doesn't allow using contract programming, i.e. the requires keyword. The compiler gives a compile-time error that looks like: test.vala:5.5-5.12: error: syntax error, expected `{'
    requires (test_value > 1)
    ^^^^^^^^
Compilation failed: 1 error(s), 0 warning(s)

The source code that created the error above is attached. (And yes, I know it doesn't have the main method, that is unimportant for this test case.)

Why would one want to use contract programming on a constructor? Because one would want to make sure that the parameters/arguments are what they are supposed to be. Of course, the simple requires (...) on a constructor isn't much more than a simple assert(...) at the beginning of the constructor, but if Vala is "advertised" to have this capability, it should. :)