MATLAB: Do I get an error generating code from a MATLAB class that can conditionally assign multiple data types to one of its properties in MATLAB Coder 2.2 (R2012a)

matlab coder

I have created a MATLAB Class called 'sampleClass' which contains a property called 'sampleProperty'. The class is initialized with a single argument 'caseNum' as follows:

function obj = sampleClass(caseNum)
      if caseNum == 1
          obj.sampleProperty = uint8(1);
      else
          obj.sampleProperty = uint16(1);
      end
end

In this way, the property is assigned to a uint8 data type if 'caseNum' is 1, and a uint16 data type otherwise. This works without any issues in MATLAB, but when I use MATLAB Coder 2.2 (R2012a) to generate code using this class, I get the following error:

 ??? Class mismatch (uint8 ~= uint16).
 The class to the left is the class of the left-hand side of the assignment.

Is there any way I can work around this?

Best Answer

The ability to assign a different data type to the property of a MATLAB Class based on some conditional statement is not supported for code generation using MATLAB Coder 2.2 (R2012a).

As a workaround, you can create two different properties of different data types and include the appropriate logic in your code to use the correct property based on this conditional statement.

Related Solutions

MATLAB: Can’t I use an Enumerated data type inherited from int32 as a logical value in an IF statement when generating code using MATLAB Coder 2.2 (R2012a)

This is expected behavior of enumerated classes inherited from the int32 data type in MATLAB Coder 2.2 (R2012a). Implicit casting to int32 is not observed in IF statements.

As a workaround, please use one of the three alternatives listed above in your MATLAB file.

MATLAB: How are objects converted from one type to another when collected together in an array in MATLAB 7.6 (R2008a)

When MATLAB sees a subscripted assignment to an existing variable, MATLAB checks the class of the right-hand-side against the class of the left-hand-side (LHS) variable. If different, it attempts to convert the right-hand-side (RHS) variable to the type of the LHS class.

To achieve this, MATLAB first looks for a method of the RHS class that has the same name as the LHS class. This is a converter method from one class to another and similar in some ways to a cast operator in C++.

If there is no specific converter, then MATLAB calls the LHS constructor and passes the RHS variable as input. This is irrespective of the class relationship between the LHS and RHS variable.

In the above example, the LHS class is SuperClass and the RHS class is SubClass. When the following line is executed,

vec(2) = subobj

since SubClass does not have a method SuperClass, MATLAB calls the SuperClass constructor with subobj as the single input, resulting in an error.

To facilitate the conversion from SubClass to SuperClass, you can create a method named SuperClass in class SubClass with the following signature

function obj = SuperClass(subobj)
      obj = SuperClass(subobj.prop1, subobj.prop2);
end

Alternatively, you can modify the constructor of SuperClass to accommodate single inputs of type SuperClass. One implementation of the constructor could be,

function obj = SuperClass(prop1, prop2)
      if isa(prop1,'SuperClass')
          obj.prop1 = prop1.prop1;
          obj.prop2 = prop1.prop2;
      else
          obj.prop1 = prop1;
          obj.prop2 = prop2;
      end
end

One drawback of the previous methods is that a copy of the object is created.

As an alternative, you can preserve the original class of the objects and still aggregate the objects by using a cell array as follows:

vec{1} = supobj;
vec{2} = subobj;

Best Answer

Related Solutions

MATLAB: Can’t I use an Enumerated data type inherited from int32 as a logical value in an IF statement when generating code using MATLAB Coder 2.2 (R2012a)

MATLAB: How are objects converted from one type to another when collected together in an array in MATLAB 7.6 (R2008a)

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