EC
StopIteration
RubyINFOCriticalIteration

External iterator has no more values

Quick Answer

Use loop{} with an enumerator — it automatically rescues StopIteration to terminate cleanly.

What this means

Raised by Enumerator#next when there are no more elements. Unlike most exceptions, StopIteration is used as flow control for external iterators and is caught internally by loop{}.

Why it happens
  1. 1Calling Enumerator#next after all elements have been exhausted
  2. 2Manual external iteration without a termination check

Fix

Use loop to automatically handle StopIteration

Use loop to automatically handle StopIteration
enum = [1, 2, 3].each
loop do
  puts enum.next
end
# prints 1, 2, 3 then exits cleanly

Why this works

Kernel#loop rescues StopIteration internally and breaks out of the loop when the enumerator is exhausted.

Code examples
Manual next raises StopIterationruby
e = [1, 2].each
e.next   # => 1
e.next   # => 2
e.next   # StopIteration: iteration reached an end
loop handles it automaticallyruby
loop { puts [1,2].each.next }  # loops safely
ClosedQueueError subclassruby
q = Queue.new
q.close
q.next rescue ClosedQueueError  # subclass of StopIteration
Sources
Official documentation ↗

Ruby Core Documentation

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