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matlabclassmex
Tom Carpenter
Tom Carpenter

Reputation: 571

MATLAB Mex C API Check if mxarray is base class

We are using classes in MATLAB which are passed into some C Mex functions. Previously the class objects we have been passing were all the same type, so we have been able to use mxIsClass to verify that the objects are the correct type.

We have however changed the architecture such that the objects are now derived from the original base class to allow customisation. Effectively we have something like:

handle & mixin.Heterogeneous>
    BaseClass >
        Class1
        Class2

Because the base class uses mixin.Heterogeneous, if I pass an array like [Class1_obj Class2_obj], the mex function works as expected - MATLAB treats the array as an array of type BaseClass, and mxIsClass(obj, 'BaseClass') returns true.

The problem arises that when we pass a single object or an array of the same derived class, say [Class1_obj1 Class1_obj2], into the mex function. Because they are the same type, MATLAB treats the array as type Class1, and so mxIsClass(obj, 'BaseClass') returns false because it only considers the class of the object and not the classes it derives from.

I'm trying to figure out if there is a way to get around this problem and make sure that the mxArray* object in the mex function is either a BaseClass directly, or derives from it.

I've considered simply adding checks for every known derived class name, but this seems an ugly way of doing this, not least because if we add more derived classes we need to change the mex function every time.

I suppose I could use the mexCallMATLAB function to call isa in MATLAB which should correctly identify that it is a base class.

I wonder also if there is a way to get MATLAB to pass the object through to the Mex function treating it as a BaseClass object rather than the derived class.


Is there a standard way of acheiving this?

Upvotes: 2

Views: 143

Answers (1)

Tom Carpenter
Tom Carpenter

Reputation: 571

MATLAB's built in isa function can be used to find out if the object or object array is the correct type. The MATLAB function does look at base clases, so doing isa(Class1_obj,'BaseClass') does return true.

I've implemented a function in the mex file that simply calls MATLAB's own isa function to check the type. As a reference for anyone with similar issues, the following is the C function I've written for this task.

    //Check the type of class object or object array using MATLAB
    static bool isa(mxArray* obj, const char* type) {
        //Create LHS/RHS arrays for calling MATLAB
        mxArray *lhs[1];
        mxArray *rhs[2];
        //Return value
        bool retVal;
        //Populate Inputs to MATLAB isa
        rhs[0] = obj;
        rhs[1] = mxCreateString(type);
        //Call the MATLAB isa function
        mexCallMATLAB(1, lhs, 2, rhs, "isa");
        //Extract result
        retVal = mxIsLogicalScalarTrue(lhs[0]);
        //Cleanup
        mxDestroyArray(rhs[1]);
        mxDestroyArray(lhs[0]);
        //Done
        return retVal;
    }

Upvotes: 3

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