Converting Matlab function to mex with user defined class object

I need to create a mex file of a function. One of the arguments of the function is the matlab user defined class object. When I try to convert the function to mex, it gives me an error that the function input does not have valid type and user defined class is not supported by coder.type. Is there any solution to this?

[Adam]

I think you can convert the class to a struct to retain its properties, but lose its functions which are obviously not transferable to mex.

I can't remember off-hand how to do this though so you could probably search for that as fast as I could!

[Guillaume]

To convert an object to a struct:

s = struct(obj);

[Adam]

Oh yeah...that was too obvious to remember!

[Amit]

Thanks Adam and Guillaume. DO you know any simpler method to convert structure back to user defined matlab class object? I can assign manually all the properties of the object with structure but as there are more that 50 properties it is tedious and perhaps will make simulation slower again.

[Guillaume]

Answer to this question, in the answers below

Answer 1

[Ryan Livingston]

Edit: As of MATLAB R2017a value objects can be inputs and outputs from MEX files.

In earlier releases, MATLAB Coder does not support the input or output arguments of the MEX function being MATLAB objects. One other option you have is to pass the values to the MEX function needed to construct the object and construct the object inside the function being passed to codegen. So rather than:

function y = foo(myObj)
<code>

you could use:

function y = foo(arg1,arg2,arg3,)
myObj = MyClass(arg1,arg2,arg3);
<code>

Then you can use the object as before in the code and still generate MEX from the function.

Using the struct approach, you could pass in the struct and then re-create the object from the struct inside of the function.

[Matt J]

Edit: As of MATLAB R2017a value objects can be inputs and outputs from MEX files.

Are there any relevant documentation links with examples that you could provide?

Answer 2

[Guillaume]

To convert a structure back to an object you can do the following function

function object = propfromstruct(object, s)
  for fieldname = fieldnames(s)'
    try
       o.(fieldname) = s.(fieldname);
    catch ex
       warning('could not copy field %s due to error %s', fieldname, ex.message);
    end
  end
end

[Dalia Sobhy]

Hello

It is not working