Functions Used with Objects

Functions to Query Class Members

These functions provide information about object class members.

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Functions to Test Objects

These functions provide logical tests, which are useful when using objects in ordinary functions.

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Using Switch/Case Statements with Objects

MATLAB enables you to use objects in switch and case expression if the object's class defines an eq method. The eq method implements the == operation on objects of that class.

For objects, switch_expression == case_expression defines how MATLAB evaluates switch and cases statements.

Handle Objects in Switch Statements

All classes derived from the handle class inherit an eq method. The expression,

h1 == h2

is true if h1 and h2 are handles for the same object.

For example, assume the BasicHandle class is defined as:

classdef BasicHandle < handle
   properties
      Prop1
   end
   methods
      function obj = BasicHandle(val)
         if nargin > 0
            obj.Prop1 = val;
         end
      end
   end
end

Create a BasicHandle object:

h1 = BasicHandle('Handle Object');
h2 = h1;
switch h1
   case h2
      disp('h2 is selected')
   otherwise 
      disp('h2 not selected')
end

The result is:

h2 is selected

Object Must Be Scalar

The switch statements work only with scalar objects. For example,

h1(1) = BasicHandle('Handle Object');
h1(2) = BasicHandle('Handle Object');
h1(3) = BasicHandle('Handle Object');
h2 = h1;
switch h1
   case h2
      disp('h2 is selected')
   otherwise 
      disp('h2 not selected')
end
SWITCH expression must be a scalar or string constant.

In this case, h1 is not scalar. Use isscalar to determine if an object is scalar before entering a switch statement.

Defining the eq Method

Enable the use of value-class objects in switch statements by implementing an eq method for the class. Use the eq method to determine what constitutes equality of two object of the class.

Behave Like a Built-in Type.  Some MATLAB functions also use the built-in == operator in their implementation. Therefore, your implementation of eq should be replaceable with the built-in eq to the extent you want to support similar behaviors and to enable objects of your class work like built-in types in MATLAB code.

Design of eq.  Implement the eq method to return a logical array representing the result of the == comparison.

For example, the SwitchOnVer class implements an eq method that returns true for the == operation if the value of the Version property is the same for both objects. In addition, eq works with arrays the same way as the built-in eq. For the following expression:

obj1 == obj2

The eq method works like this:

• If both obj1 and obj2 are scalar, eq returns a scalar value.

• If both obj1 and obj2 are nonscalar arrays, then these arrays must have the same dimensions, and eq returns an array of the same size.

• If one input argument is scalar and the other is a nonscalar array, then eq treats the scalar object as if it is an array having the same dimensions as the nonscalar array.

Implementation of eq.  Here is a class that implements an eq method. Ensure your implementation contains appropriate error checking for the intended use.

classdef SwitchOnVer
   properties
      Version
   end
   methods
      function obj = SwitchOnVer(ver)
         if nargin > 0
            obj.Version = ver;
         end
      end
      function bol = eq(obj1,obj2)
         if ~strcmp(class(obj1),class(obj2))
            error('Objects are not of the same class')
         end
         s1 = numel(obj1);
         s2 = numel(obj2);
         if s1 == s2
            bol = false(size(obj1));
            for k=1:s1
               if obj1(k).Version == obj2(k).Version
                  bol(k) = true;
               else
                  bol(k) = false;
               end
            end
         elseif s1 == 1
            bol = scalarExpEq(obj2,obj1);
         elseif s2 == 1
            bol = scalarExpEq(obj1,obj2);
         else
            error('Dimension missmatch')
         end
         function ret = scalarExpEq(ns,s)
            % ns is nonscalar array
            % s is scalar array
            ret = false(size(ns));
            n = numel(ns);
            for kk=1:n
               if ns(kk).Version == s.Version
                  ret(kk) = true;
               else
                  ret(kk) = false;
               end
            end
         end
      end
   end
end

Use SwitchOnVer objects in switch statements by comparing known versions with the object being compared:

% Create known versions of objects
ov1 = SwitchOnVer(1.0);
ov2 = SwitchOnVer(2.0);
ov3 = SwitchOnVer(3.0);
...

...
if isscalar(objIn)
      switch(objIn)
         case ov1
            disp('This is version 1.0')
         case ov2
            disp('This is version 2.0')
         case ov3
            disp('This is version 3.0')
         otherwise
            disp('There is no version')
      end
   else
      error('Input object must be scalar')
   end

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Understanding MATLAB Code Analyzer Warnings

Using the Editor and Debugger with Classes

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