Enumerator is an object that implements iteration in a controlled fashion.
Instead of looping until some condition is satisfied, the object enumerates values as needed. Execution of the loop is paused until the next value is requested by the owner of the object.
Enumerators make infinite streams of values possible.
|Responds to |
Let's create an
Enumerator for Fibonacci numbers.
fibonacci = Enumerator.new do |yielder| a = b = 1 loop do yielder << a a, b = b, a + b end end
We can now use any
Enumerable method with
fibonacci.take 10 # => [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
If an iteration method such as
each is called without a block, an
Enumerator should be returned.
This can be done using the
def each return enum_for :each unless block_given? yield :x yield :y yield :z end
This enables the programmer to compose
each.drop(2).map(&:upcase).first # => :Z
rewind to restart the enumerator.
ℕ = Enumerator.new do |yielder| x = 0 loop do yielder << x x += 1 end end ℕ.next # => 0 ℕ.next # => 1 ℕ.next # => 2 ℕ.rewind ℕ.next # => 0