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@AndrewO
Created May 2, 2013 21:52
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Lazily adding information to Ruby's Enumerator's.
module Enumerator::WithFinal
# Emits a boolean indicating whether or not the current iteration is the final one.
def self.with_final(prev_enum)
begin
while next_val = prev_enum.next
is_final = begin
prev_enum.peek
rescue StopIteration
true
else
false
end
yield [next_val, is_final]
end
rescue StopIteration
end
end
# If you like monkeypatching Ruby's standard library, go for it.
def with_final
Enumerator.new {|y| Enumerator::WithFinal.with_final(self) {|*v| y << v } }
end
end
if __FILE__ == $0
require "minitest/spec"
require "minitest/autorun"
describe Enumerator::WithFinal do
it "chains well with others" do
r = 1..10
Enumerator::WithFinal.with_final(r.each.with_object("foo").with_index) do |*args|
val, foo, i, is_final = args.flatten
# puts "val, i, foo, is_final: #{val}, #{i}, #{foo}, #{is_final}"
assert_equal(val, i + 1)
assert_equal(is_final, i == r.end - 1)
end
end
it "monkeypatches" do
class Enumerator
include Enumerator::WithFinal
end
r = 1..10
r.each.with_object("foo").with_index.with_final.each do |*args|
val, foo, i, is_final = args.flatten
# puts "val, i, foo, is_final: #{val}, #{i}, #{foo}, #{is_final}"
assert_equal(val, i + 1)
assert_equal(is_final, i == r.end - 1)
end
end
end
end
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