gistfile1.rb

class PagingEnumerator < Enumerator
  def initialize(&block)
    super do |yielder|
      page = 0
      loop do
        items = block.call(page)
        break if items.empty?
        items.each {|item| yielder.yield(item) }
        page += 1
      end
    end
  end

  def lazy_reject(&block)
    Enumerator.new do |yielder|
      each do |object|
        yielder.yield(object) unless block.call(object)
      end
    end
  end
end


describe PagingEnumerator do
  it "iterates through each page" do
    enumerator = PagingEnumerator.new {|page| [1, 2, 3] }
    enumerator.take(6).should == [1, 2, 3, 1, 2, 3]
  end

  it "passes a page number to the block" do
    enumerator = PagingEnumerator.new {|page| [page] }
    enumerator.take(3).should == [0, 1, 2]
  end

  it "stops at a blank page" do
    enumerator = PagingEnumerator.new {|page| page == 0 ? [1, 2, 3] : [] }
    enumerator.take(6).should == [1, 2, 3]
  end

  context "#lazy_reject" do
    it "rejects objects that for which the block returns true" do
      enumerator = PagingEnumerator.new {|page| [1, 2, 3] }
      enumerator.lazy_reject {|n| n == 2 }.take(6).should == [1, 3, 1, 3, 1, 3]
    end
  end
end