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module Enumerable class StopIteration < IndexError end class Enumerator include Enumerable def initialize(obj, method = :each, *args) @obj = obj @meth = method @iter = method(method) end def each(&block) if block_given? @obj.each(&block) else self end end def with_index n = 0 each do |e| yield(e, n) n += 1 end end alias each_with_index with_index def next # Generator end def rewind # Generator end end def each_slice(n) raise(ArgumentError, "invalid slice size") if n <= 0 sum = [] each do |e| sum.push(e) if sum.size == n yield(sum) sum = [] end end yield(sum) if sum.size > 0 return nil end alias enum_slice each_slice def each_cons(n) raise(ArgumentError, "invalid size") if n <= 0 sum = [] each do |e| sum.shift if sum.size == n sum.push(e) if sum.size == n yield(sum) end end return nil end alias enum_cons each_cons end module Kernel def enum_for(*args) Enumerable::Enumerator.new(self, *args) end alias to_enum enum_for end [1,2,3].enum_for(:each).map{|n| n + 1 } [1,2,3].enum_for(:each).with_index{|n, i| p n => i } puts '', "each_cons(3):" (1..10).each_cons(3){|n| p n } puts '', "each_slice(3):" (1..10).each_slice(3){|n| p n }

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