Fun with Enumerator

Fun with Ruby's Enumerator class

Transcript

1. Fun* with Enumerator (*may not be fun)
2. Enumerator != Enumerable [1, 2, 3].each => #<Enumerator: [1, 2, 3]:each> [1, 2, 3].map => #<Enumerator: [1, 2, 3]:map> [1, 2, 3].select => #<Enumerator: [1, 2, 3]:select>
3. It gets weird enum = [1, 2, 3].map => #<Enumerator: [1, 2, 3]:map> enum.each { |n| "<#{n}>" } => ["<1>", "<2>", "<3>"]
5. We can make our own Enumerators enum = Enumerator.new do |yielder| yielder.yield 1 yielder.yield 2 end enum.to_a => [1, 2]
6. enum = Enumerator.new do |yielder| puts "Beginning" yielder.yield 1 puts "Middle" yielder.yield 2 puts "End" end enum.next Beginning => 1 enum.next Middle => 2 enum.next End StopIteration: iteration reached an end
7. Infinite sequences! fib = Enumerator.new do |yielder| a = 0 b = 1 loop do yielder.yield b tmp = a a = b b = tmp + b end end fib.first 10 => [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
8. Extending Enumerable module Enumerable def my_with_index Enumerator.new do |yielder| i = 0 self.each do |e| yielder.yield e, i i += 1 end end end end [:foo, :bar, :baz].my_with_index do |e, i| puts "#{i}: #{e}" end.to_a => [[:foo, 0], [:bar, 1], [:baz, 2]]
9. Miscellany • Use .lazy when working with infinite series • Useful for managing expensive operations • Does not implement a cache (See CachingEnumerator gem)
10. Questions?