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module Enumerable
# = Enumerable#lazy implementation
#
# Enumerable#lazy returns an instance of Enumerable::Lazy.
# You can use it just like as normal Enumerable object,
# except these methods act as 'lazy':
#
# - map collect
# - select find_all
# - reject
# - grep
# - drop
# - drop_while
# - take_while
# - flat_map collect_concat
# - zip
def lazy
Lazy.new(self)
end
# == Acknowledgements
#
# Based on https://github.com/yhara/enumerable-lazy
# Inspired by https://github.com/antimon2/enumerable_lz
# http://jp.rubyist.net/magazine/?0034-Enumerable_lz (ja)
class Lazy < Enumerator
def initialize(obj, &block)
super(){|yielder|
begin
obj.each{|x|
if block
block.call(yielder, x)
else
yielder << x
end
}
rescue StopIteration
end
}
end
def map(&block)
Lazy.new(self){|yielder, val|
yielder << block.call(val)
}
end
alias collect map
def select(&block)
Lazy.new(self){|yielder, val|
if block.call(val)
yielder << val
end
}
end
alias find_all select
def reject(&block)
Lazy.new(self){|yielder, val|
if not block.call(val)
yielder << val
end
}
end
def grep(pattern)
Lazy.new(self){|yielder, val|
if pattern === val
yielder << val
end
}
end
def drop(n)
dropped = 0
Lazy.new(self){|yielder, val|
if dropped < n
dropped += 1
else
yielder << val
end
}
end
def drop_while(&block)
dropping = true
Lazy.new(self){|yielder, val|
if dropping
if not block.call(val)
yielder << val
dropping = false
end
else
yielder << val
end
}
end
def take(n)
if n == 0
return Lazy.new(self){raise StopIteration}
end
taken = 0
Lazy.new(self){|yielder, val|
yielder << val
taken += 1
if taken >= n
raise StopIteration
end
}
end
def take_while(&block)
Lazy.new(self){|yielder, val|
if block.call(val)
yielder << val
else
raise StopIteration
end
}
end
def flat_map(&block)
Lazy.new(self){|yielder, val|
ary = block.call(val)
# TODO: check ary is an Array
ary.each{|x|
yielder << x
}
}
end
alias collect_concat flat_map
def zip(*args, &block)
enums = [self] + args
Lazy.new(self){|yielder, val|
ary = enums.map{|e| e.next}
if block
yielder << block.call(ary)
else
yielder << ary
end
}
end
alias force to_a
end
end
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