## Copyright (C) 2004-2018 Paul Kienzle
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <https://www.gnu.org/licenses/>.
##
## Original version by Paul Kienzle distributed as free software in the
## public domain.

## -*- texinfo -*-
## @deftypefn {} {} inputname (@var{n})
## Return the name of the @var{n}-th argument to the calling function.
##
## If the argument is not a simple variable name, return an empty string.  As
## an example, a reference to a field in a structure such as @code{s.field} is
## not a simple name and will return @qcode{""}.
##
## @code{inputname} is only useful within a function.  When used at the command
## line it always returns an empty string.
## @seealso{nargin, nthargout}
## @end deftypefn

function name = inputname (n)

  if (nargin != 1)
    print_usage ();
  endif

  name = "";
  try
    name = evalin ("caller", sprintf ("__varval__ ('.argn.'){%d}", fix (n)));
  catch
    return;
  end_try_catch

  ## For compatibility with Matlab,
  ## return empty string if argument name is not a valid identifier.
  if (! isvarname (name))
    name = "";
  endif

endfunction


## Warning: heap big magic in the following tests!!!
## The test function builds a private context for each test, with only the
## specified values shared between them.  It does this using the following
## template:
##
##     function [<shared>] = testfn (<shared>)
##        <test>
##     endfunction
##
## To test inputname, I need a function context invoked with known parameter
## names.  So define a couple of shared parameters, et voila!, the test is
## trivial.

%!shared hello, worldly
%!assert (inputname (1), "hello")
%!assert (inputname (2), "worldly")
%!assert (inputname (3), "")

## Clear parameter list so that testfn is created with zero inputs/outputs
%!shared
%!assert (inputname (-1), "")
%!assert (inputname (1), "")

%!function r = __foo__ (x, y)
%!  r = inputname (2);
%!endfunction
%!assert (__foo__ (pi, e), "e")
%!assert (feval (@__foo__, pi, e), "e")

%!error inputname ()
%!error inputname (1,2)
