Difference between type and class in fortran 2003

Question

I have been told for my PhD that I have to learn fortran 2003 language. I have never used and OOP program before nor fortran. I am trying to understand what the difference between type and class is. I know that classes are declared with the 'TYPE' keyword but I have also seen examples of the keyword 'CLASS' being used used so I am getting confused. Hope that makes sense.

Answer 1

The keyword type is used to declare derived types -- best not to get into the habit of thinking, perhaps imported from foreign languages, that type is used for declaring something called classes.

The keyword class is used, in restricted circumstances, to mean of the type specified or any of its extended types. extended type is Fortran-speak for a type which extends another type, essentially one which specialises or inherits from another type. The restricted circumstances within which class is used are in procedure dummy-argument lists and in declarations of entities with the attribute allocatable or the attribute pointer. A class entity gets a dynamic type at run-time, and its dynamic type may vary from run to run, or across a single execution of the program.

If you don't understand the explanation in the previous paragraphs it's possibly because I've explained things poorly, but it's also possibly because you don't yet have enough of a grounding in the basics of Fortran. To acquire the grounding find yourself an up-to-date online tutorial, an online reference guide, and start programming.