Fill Items and Prototypes

Every array has an associated prototype which is derived from the array's first item. If the first item is a (ref to) an Instance of a Class, the prototype is a ref to that Class.

Fill items for an overtake operation, are derived from the argument's prototype.

For each Class reference in the prototype, there is a ref to a (newly constructed and distinct) instance of that Class that is initialised by the niladic (default) constructor for that Class, if defined.

      2↑⎕NEW MyClass
 #.[Instance of MyClass]  #.[Instance of MyClass]

Note that in the above example, two distinct instances are constructed (the first by ⎕NEW and the second by the overtake).

Fill items are used in a number of operations including:

• First (⊃ or ↑) of an empty array
  
  
• Fill-elements for overtake
  
  
• For use with the Each operator on an empty array