The empty method enables you to initialize arrays of a specific class:

C = char.empty(0,7)

C =

   Empty matrix: 0-by-7

disp(class(C))
char

Initializing an array with empty brackets ([]) produces an empty array of class double:

a = [];

disp(class(a))
double

You can initialize an empty array of a user-defined class. For example, the empty static method is a hidden method of the RGBColor class defined here.

classdef ColorInRGB
   properties
      Color (1,3) = [1,0,0];
   end
   methods
      function obj = ColorInRGB(c)
         if nargin > 0
            obj.Color = c;
         end
      end
   end
end

To create an empty 0-by-5 array of class ColorInRGB, call the empty method:

A = ColorInRGB.empty(0,5);

You can use the isempty, size, and length functions to identify empty object arrays. For example, create an empty array of the ColorInRGB class defined in the previous section.

A = ColorInRGB.empty(0,5);
isempty(A)

ans =

  logical

   1

size(A)

ans =

     0     5

length(A)

ans =

     0

Empty arrays follow array concatenation behavior. For example, create an empty array of the ColorInRGB class defined in the previous section and for a new array by concatenating instances into another array.

A = ColorInRGB.empty(0,5);
B = [A A]

B = 

  0×10 ColorInRGB array with properties:

    Color

You cannot index into an empty array.

B(0,3)

Index in position 1 is invalid. Array indices must be positive integers or logical values.