Doing something repeatedly.
THE TWO KINDS
Iterating over a collection, and repeating while a condition holds.
WHICH TO USE
Iterating over a collection, almost always.
WHY
It is clearer and cannot loop forever by accident.
WHEN TO USE A CONDITIONAL LOOP
When you do not know in advance how many repetitions are needed.
WHAT TO BE CAREFUL WITH
Loops that may never end Modifying the collection you are iterating over Doing expensive work inside a loop that could be done once
THAT LAST POINT
The most common cause of slow scripts.
BREAKING OUT EARLY
Possible, and useful when you have found what you wanted.
SKIPPING AN ITERATION
Also possible, and frequently clearer than nesting a condition.
ITERATING WITH POSITIONS
Available when you need both the item and its index.
NESTED LOOPS
Multiply the work.
A loop inside a loop over large collections becomes slow quickly.
WHAT TO CONSIDER INSTEAD
Whether the work can be done in one pass.
