rivets.adapters[':'] =
  observe: (obj, keypath, callback) ->
    obj.on('change:' + keypath, callback)
  unobserve: (obj, keypath, callback) ->
    obj.off('change:' + keypath, callback)
  get: (obj, keypath) ->
    obj.get(keypath)
  set: (obj, keypath, value) ->
    obj.set(keypath, value)
rivets.formatters['first-letter'] = (value) ->
  if value? then value.charAt(0) else ' '
rivets.formatters['only'] = (value, allowed...) ->
  if value in allowed then value else ''
rivets.formatters['eq'] = (a, b) ->
  a is b
rivets.formatters['format-date'] = (value, format) ->
  if value? then value.format(format) else ''
rivets.formatters['iso-date'] = (value) ->
  if value? then value.toISOString() else ''
rivets.formatters['from-now'] = (value) ->
  if value? then value.fromNow() else ''