Generics: What's a “CONSTRUCTOR constraint”?

Question

I made a custom TObjectList descendant designed to hold subclasses of a base object class. It looks something like this:

interface
   TMyDataList

        

Answer 1

You're trying to create an instance of T via T.Create. This doesn't work because the compiler doesn't know that your generic type has a parameterless constructor (remember: this is no requirement). To rectify this, you've got to create a constructor constraint, which looks like this:

or, in your specific case: