Iterators

Context:

    Classes
    ValueTypes 
    Interfaces
        Type Members

iterator-specification

iterator-header

Example

Here we use an iterator-id paragraph GetEven to return the even numbers in the m-FibonacciArray

       class-id Fibonacci.Class1 static.

       data division.
       working-storage section.
       01 m-FibonacciArray binary-long occurs any static.
       method-id FibEvens static.
       procedure division.
        set content of m-FibonacciArray to (1 2 3 5 8 13 21 34 55 89 144)

        display "Even numbers in the Fibonacci sequence:"         
        perform varying evenNumber as binary-long through self::GetEven
            display evenNumber
        end-perform
           goback.
       end method.

       iterator-id GetEven yielding res as binary-long static.

        perform varying i as binary-long through m-FibonacciArray
            if i b-and 1 = 0
                set res to i
                goback
            end-if
        end-perform
        stop iterator *> stops the iterator explicitly
       end iterator.  *> end of method stops the iterator implicitly 
       end class.

The following is a similar example, but uses the self syntax to allow iteration directly through the current class (that is, the class in which the iterator appears).

       class-id Fibonacci.Class2.
       method-id main static (args as string occurs any).
           try
               declare max as binary-long = binary-long::Parse(args[0])
               declare fibs = new Fibonacci(max)
               perform varying i as binary-long through fibs
                   display i
               end-perform
           catch
               display "Bad command line"
           end-try
       end method.
       end class.

       class-id Fibonacci.
       01 MaxNumber binary-long.

       method-id new (#max as binary-long).
           set MaxNumber to #max
       end method.

       iterator-id self yielding res as binary-long.
           set res to 1
           exit iterator
           declare frst as binary-long = 0
           declare second as binary-long = 1
           perform until exit
               compute res = frst + second
               if res > MaxNumber
                   stop iterator
               end-if
               move second to frst
               move res to second
               exit iterator
           end-perform
       end iterator.
       end class.

See also the Iterators sample, which is available from $COBDIR/demo.

Further information

If you specify parameters in the iterator header, you must not include a procedure division header in the body of the iterator.

The STOP ITERATOR statement stops the iteration.

This statement is not needed if the next statement is END ITERATOR.