Continued looking at properties in D - interfaces and constraints

[mikey via Digitalmars-d-learn]

Hi,

I'm continuing to look at properties in D and have found another 
area where I think there may be an issue - or maybe where I'm 
doing something wrong.

I have started trying to use constraints on my properties to 
constrain which values they can take I have also started trying 
to use interfaces. What I noticed was that when I combine these 2 
features the constraints get discarded.

    interface Widthy {
        @property inout(int) width() inout;
        @property void width(int width);
    }

    class Test : Widthy {
    private:
        int _w;
    public:
        @property inout(int) width() inout { return _w; }
        @property void width(int width)
        in {
            import std.exception;
            if (width < 0) {
                throw new
                Exception("width is less than zero");
            }
        }
        body {
            _w = width;
        }
    }

    void main() {
        import std.stdio;
        auto t = new Test;
        t.width = -1;
        writeln("width: ", t.width);
        // width: -1

        // hmmm... not good
    }