I/O and the LRM

[hal!hathor!jeffe@seismo.css.gov (Jeff Etrick)]

 The following is taken from the LRM:

>>function NAME(FILE : in FILE_TYPE) return STRING;

>>Returns a string which uniquely identifies the external file currently
>>associated with the given file (and may thus be used in an OPEN
>>operation).  If an environment allows alternative specifications of the
>>name (for example, abbreviations), the string returned by the function
>>should correspond to a full specification of the name.

>>The exception STATUS_ERROR is raised if the given file is not open.


 I have used the function successfully many times to get the external
name of a currently opened file but what I don't understand is the
comment about it being used in an open statement. Why would I want to use
this statement in an open since the file must already be opened or
STATUS_ERROR will be raised.

Thanks for the help,

Jeff