I don't see how this is in any way preferable to having an ordinary default constructor that does the same thing:

    // There are a few ways to let API callers bring their own 
    // memory, as they would in a no-malloc environment and this
    // stack-friendly c'tor is a stand-in for that. 
    static Birthdate epoch() { return Birthdate(1900, 1, 1); }