Failure semantics are the obvious ones. At the very least you'll need some flavor of

    try {
      user.them.public_keys.primary.bundle
    } rescue {
      OhDamn
    }

Less obvious is the potential for multiple targets. JWalk probably doesn't do this, but it could. For more ideas for how this could work take a look at

http://research.microsoft.com/pubs/77415/theessenceofdataacc...