Check isempty on quantities (see #11, #17): Implementation without calling *.on()

+quantity/Discrete.m

@@ -59,7 +59,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 					% quantity.Discrete
 					obj = valueOriginal;
 				else
-					% empty object. this is neede for instance, to create
+					% empty object. this is needed for instance, to create
 					% quantity.Discrete([]), which is useful for creating default 
 					% values.
 					obj = quantity.Discrete.empty(size(valueOriginal));
@@ -1594,8 +1594,18 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			% ISEMPTY checks if the quantity object is empty
 			%   empty = isempty(obj)
 			
-			% check if there is already an object
-			empty = any(size(obj) == 0) || any(cellfun(@iscell, [obj.grid]));
+			% check if there is any dimension which is zero
+			empty = any(size(obj) == 0);
+			
+			% if the constructor is called without arguments, a
+			% quantity.Discrete is initialized without an initialization of
+			% the grid. Thus, the grid is not a cell:
+			empty = empty || ~iscell(obj(1).grid);
+			
+			% in order to check this for arrays:
+			% scalar and array empty check has to be separated because the 
+			% [obj.grid] does only work in the array case.
+			empty = empty || any(cellfun(@iscell, [obj.grid]));
 			
 		end % isempty()
 		
@@ -2288,7 +2298,14 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 		% 		end
 		
 		function s = getPropertyGroups(obj)
-			s = getPropertyGroups@matlab.mixin.CustomDisplay(obj(1));
+			% Function to display the correct values
+			
+			if isempty(obj)
+				s = getPropertyGroups@matlab.mixin.CustomDisplay(obj);
+				return;
+			else
+				s = getPropertyGroups@matlab.mixin.CustomDisplay(obj(1));	
+			end
 			
 			if numel(obj) ~= 1
 				s.PropertyList.valueDiscrete = ...

+unittests/+quantity/testDiscrete.m

@@ -1246,9 +1246,16 @@ end
 
 function testIsEmpty(tc)
 
-	
+% create an empty quantity and check if it is empty:
+e = quantity.Discrete.empty([5, 0]);
+tc.verifyTrue(isempty(e));
 
-%verifyTrue(tc, isempty(quantity.Discrete()))
+% create an empty object by calling the constructor without arguements.
+tc.verifyTrue(isempty(quantity.Discrete()));
+
+% create a constant quantity.Discrete. This should not be empty:
+c = quantity.Discrete(1, 'grid', {}, 'gridName', {});
+tc.verifyTrue(~isempty(c));
 end