Iterator¶
An iterator can be obtained from Enumerable:ITERATOR
as well as from other places.
An ITERATOR is a
generic computer programming concept.
In the general case it’s a variable type that allows you to get
the value at a position in some collection, as well as increment
to the next item in the collection in order to operate on all
objects in the collection one at a time. In kOS it operates
on Lists
and most other collection types.
A loop using an Iterator
on a List
might look like this:
// Starting with a list that was built like this
SET MyList To LIST( "Hello", "Aloha", "Bonjour").
// It could be looped over like this
SET MyCurrent TO MyList:ITERATOR.
PRINT "before the first NEXT, position = " + MyCurrent:INDEX.
UNTIL NOT MyCurrent:NEXT {
PRINT "Item at position " + MyCurrent:INDEX + " is [" + MyCurrent:VALUE + "].".
}
Which would result in this output:
before the first NEXT, position = -1.
Item at position 0 is [Hello].
Item at position 1 is [Aloha].
Item at position 2 is [Bonjour].
When you first create an iterator by using an ITERATOR suffix of some collection
type like List
, List
, or even String
, the
initial position of the index is always -1, and the current value is always
invalid. This represents a position just before the start of the list of
items. Only after the first time NEXT
is called does the value of
VALUE
become usable as the first thing in the collection.
If you want to restart an iteration you must call the :ITERATOR
suffix of
the collection again to obtain a new iterator. Older versions of kOS had a :RESET
suffix but it was removed as it could not be supported on all types.
Members¶
- structure Iterator¶
¶ Suffix
Type
Description
n/a
(This method has been removed)
Move iterator to the next item
Check if iterator is at the end of the list
Current index starting from zero
varies
The object currently being pointed to
- Iterator:RESET()¶
- Returns
n/a
This suffix has been deleted from kOS.
- Iterator:NEXT()¶
- Returns
Call this to move the iterator to the next item in the list. Returns true if there is such an item, or false if no such item exists because it’s already at the end of the list.
- Iterator:ATEND¶
- Access
Get only
- Type
Returns true if the iterator is at the end of the list and therefore cannot be “NEXTed”, false otherwise.
- Iterator:INDEX¶
- Access
Get only
- Type
Scalar
(integer)
Returns the numerical index of how far you are into the list, starting the counting at 0 for the first item in the list. The last item in the list is numbered N-1, where N is the number of items in the list.
Note
If you have just created the ITERATOR, then the value of
Iterator:INDEX
is -1. It only becomes 0 after the first call toIterator:NEXT
.
- Iterator:VALUE¶
- Access
Get only
- Type
varies
Returns the thing stored at the current position in the list.