Can I find out if a class is an abstract class before trying to instantiate it?

Can i somehow say:

if isAbstract(className)

   % do something

else

% do something else

end

Answer 1

[per isakson]

A class is abstract if any of its properties or methods is abstract.

It's possible to write a function, is_abstract. Start:

    mco = ?my_class
    mco.PropertyList
    mco.MethodList

    any([mco.MethodList.Abstract])

.

or better

    mcls = meta.class.fromName('ClassName')

[Walter Roberson]

Would it be neccesary to check recursively? A method might not be obviously abstract but might call upon abstract methods ?

[per isakson]

Wouldn't calling an abstract method in a class definition be an error?

[Daniel Shub]

@Walter, but that "hidden" abstract method would be abstract and eventually caught. The metaclass object has access to all methods and properties (even private ones), so I do not think it needs to be recursive.

Answer 2

[Image Analyst]

I don't think so. But you should know just by looking at the code, or just try it and see. Why would you ever not know what you're calling and have to use the test you you described? Worst case, you could wrap your method call in a try/catch to do what you want, but I would recommend knowing beforehand than doing that.

Answer 3

[Sam]

thank you per, that did the trick.

the reason for the question was i am writing a test function that loops through all classes in a directory and instantiates them, but abstract classes were a problem.

Answer 4

[Daniel Shub]

It might be quicker to try and create the object in a try-catch and deal with errors when they happen.

Answer 5

[Kyle]

You can create a simple function to do this:

function tf = isClassAbstract(className)
    tf = meta.class.fromName(className).Abstract;
end

The Abstract property of meta.class is true "if the class or any property or method has its Abstract attribute set to true."