How to determine if an object is a built-in class?

How can I determine if an object is a built-in class?

Not only doubles, structs, strings and all those base data types but also stuff like figures, dynamic systems (tf & ss objects)

[Steven Lord]

Why? How would you handle those types of data differently than instances of classes defined by non-MathWorks code?

[Cedric Kotitschke]

I wrote an optimization toolbox which returns a solution object containing objects from this toolbox. I want to convert this to a struct so that other colleagues can view it without having access to the toolbox

Answer 1

[Steven Lord]

Okay. You could achieve your stated goal without actually having to ask "Is this an instance of my class or an instance of some other class or other data type?" If you had a method named struct for your class, or if you defined a non-Static method with some other name that accepted just one input, then the input would be an instance of your class. In the case of struct the method would be a converter method, while if it were some other name that returned a struct it would be just an ordinary instance method.

Or if you do need to ask if the object is an instance of one of the classes you created, you don't need to ask the broad question "Is this an instance of a type MathWorks provided?" You could ask a more targeted question, asking if the variable isa instance of one of your classes.

[Cedric Kotitschke]

I was trying to find a universal way to avoid specifying classes that I want to convert so that it can be applied to any custom tool anybody will write in the future. I ended up using this method but it feels ugly and is not very efficient:

function tf = isbuiltin(object)
    tf = startsWith(which(class(object)), matlabroot) || ...
        contains(which(class(object)), 'built-in');
end

[Steven Lord]

I was trying to find a universal way to avoid specifying classes that I want to convert so that it can be applied to any custom tool anybody will write in the future.

So you want to write a function that can accept any array and turn it into a struct? That's a very tall order.

Instead what I would focus on would be overloading struct for your classes. That way you can convert only the pieces of the object that users need to know about (leaving out any internal implementation details.) You could probably delegate some of that work to the built-in struct function and prune out any internal properties that shouldn't be included in the struct.

c = onCleanup(@() disp('bye')) % object in MATLAB without a struct overload

c = 
  onCleanup with properties:

    task: @()disp('bye')

which -all struct(c)

built-in (/MATLAB/toolbox/matlab/datatypes/struct/struct)

s1 = struct(c) % Call the built-in function; note the warning

Warning: Calling STRUCT on an object prevents the object from hiding its implementation details and should thus be avoided. Use DISP or DISPLAY to see the visible public details of an object. See 'help struct' for more information.

s1 = struct with fields:
    task: @()disp('bye')

s2 = builtin('struct', c) % Would call the built-in even if there's an overload

Warning: Calling STRUCT on an object prevents the object from hiding its implementation details and should thus be avoided. Use DISP or DISPLAY to see the visible public details of an object. See 'help struct' for more information.

s2 = struct with fields:
    task: @()disp('bye')