.. efun:: mapping map_indices(mapping m, string func, string|object ob, ...)
  mapping map_indices(mapping m, closure cl, ...)

  ``ob->func()`` is called resp. cl applied to every element in the mapping, with the key of the element as first argument, and then the extra args that were given to map_indices (these args must not be protected references like &(i[0])). The data item in the mapping is replaced by the return value of the function. ob can also be a file_name of an object.

  If :arg:`ob` is omitted, or neither a string nor an object, it defaults to ``this_object()``.

  Note that if mapping m has more than one value per key, these are ignored: the resulting mapping always has one value per key.

  Also note that the behaviour of this function is different from ``map(<array>)``.

  .. usage::

    ::

      m = mkmapping(users());
      m = map_indices(m, #'environment);

  :history 3.2.6 introduced: renamed from ``map_mapping()`` and complemented by :efun:`map`.

  .. seealso:: :efun:`map`, :efun:`filter`, :efun:`filter_indices`, :efun:`walk_mapping`, :efun:`member`, :efun:`m_contains`