stop with error when length operator is used. closes #35

src/@dseries/length.m

+function length(o)
+
+% Overloads size function.
+
+% Copyright (C) 2017 Dynare Team
+%
+% This file is part of Dynare.
+%
+% Dynare 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.
+%
+% Dynare 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 Dynare.  If not, see <http://www.gnu.org/licenses/>.
+
+error(['dseries::length: we do not support the length operator on ' ...
+       'dseries. Please use ''nobs'' or ''vobs''']);
+
+%@test:1
+%$ % Define a dates object
+%$ ts = dseries(randn(10,1));
+%$ try
+%$     p = length(ts)
+%$     t(1) = false;
+%$ catch
+%$     t(1) = true;
+%$ end
+%$
+%$ T = all(t);
+%@eof:1
\ No newline at end of file

src/@dseries/subsref.m

@@ -85,6 +85,9 @@ switch S(1).type
       case 'freq'
         % Returns an integer characterizing the data frequency (1, 4, 12 or 52)
         B = A.dates.freq;
+      case 'length'
+        error(['dseries::subsref: we do not support the length operator on ' ...
+               'dseries. Please use ''nobs'' or ''vobs''']);
       case 'save'                                                        
         % Save dseries object on disk (default is a mat file).
         B = NaN;