> almost zero mainstream (statically typed) programming languages can even let you write down that you want a non-empty string.

Today D will fulfill your dreams!

    struct MyString {
        private string s = "error";
        alias s this;

        this(string s) {
            assert(s.length);
            this.s = s;
        }
    }


    void main() {
        MyString ms = "hello";
        test(ms);
        MyString mserror = ""; // runtime assert fail
    }

    void test(string s) { }