How to obtain static member variables in MATLAB classes?

Question

Is there a way to define static member variables in MATLAB classes?

This doesn\'t work:

classdef A

    properties ( Static )
        m = 0;
    end
         


        

Answer 1

Here's a direct way to create a static property in Matlab. The only difference between this implementation and a hypothetical (but impossible; see Mikhail's answer) true static property is the syntax for setting the member variable.

classdef StaticVarClass
    methods (Static = true)
        function val = staticVar(newval)
            persistent currentval;
            if nargin >= 1
                currentval = newval;
            end
            val = currentval;
        end
    end
end

Now the static property staticVar can be read via:

StaticVarClass.staticVar

...and be set via:

StaticVarClass.staticVar(newval);

So, for instance, this is the expected output from a test of this functionality:

>> StaticVarClass.staticVar
  ans =
      []
>> StaticVarClass.staticVar('foobar')
  ans =
      foobar
>> StaticVarClass.staticVar
  ans =
      foobar
>> 

This approach works just as well for private static properties like you requested, but the demo code is a little longer. Note that this is not a handle class (though it would work perfectly well on a handle class as well).

classdef StaticVarClass
    methods (Access = private, Static = true)
        function val = staticVar(newval)
            persistent currentval;
            if nargin >= 1
                currentval = newval;
            end
            val = currentval;
        end
    end

    methods
        function this = setStatic(this, newval)
            StaticVarClass.staticVar(newval);
        end

        function v = getStatic(this)
            v = StaticVarClass.staticVar;
        end
    end
end

...and the test:

>> x = StaticVarClass
  x = 
      StaticVarClass with no properties.
      Methods
>> x.getStatic
  ans =
      []
>> x.setStatic('foobar')
  ans = 
      StaticVarClass with no properties.
      Methods
>> x.getStatic
  ans =
      foobar
>>