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11.2.1 Overview of default objects and classes ¶

The object–oriented programming facilities implemented by MBFL have the following core concepts:

• The object system implements single–inheritance.
• The object mbfl_default_object is a class; it is the default top superclass of classes in MBFL.
• We define new classes by subclassing from mbfl_default_object.
• We define new objects by instantiating a subclass of mbfl_default_object.
• The class mbfl_default_object has itself a class, called metaclass, it is mbfl_default_abstract_class. A class has mbfl_default_object as superclass if and only if: its metaclass is mbfl_default_class or its metaclass is a subclass of mbfl_default_class.
• Every instance of class mbfl_default_object has the layout specified by mbfl_default_object.
• The class mbfl_default_object and its subclasses have the layout specified by mbfl_default_class.
• Every instance of mbfl_default_object is a Bash index array with the following layout:

  instance[0] ⇒ _(SUBCLASS_OF_MBFL_DEFAULT_OBJECT)
  instance[1] ⇒ 1st field value
  instance[2] ⇒ 2nd field value
  ...
  

  an array element with key ‘0’ is always present and its value is a string; the string represents the name of an array; the array is the instance’s class definition.

• We handle instances through references: a reference is a string representing a variable name; the variable itself is an index array. We manage references using the NAMEREF mechanism, a reference is the name of a data variable; Variable name references for details.
• Default objects being arrays: they have a scope. When a local scope is left, all the resources associated with the instance, as defined by its class, are released. If an object’s field references some asynchronous resources: such resources must be released with some other mechanism.

• objects default overview objects:		Overview of default objects.
• objects default overview classes:		Overview of default classes.