This lazily initialized hash maps integers to their factorials : Hash.new « Hash « Ruby

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Ruby » Hash » Hash.new   This lazily initialized hash maps integers to their factorials fact = Hash.new {|h,k| h[k] = if k > 1: k*h[k-1] else 1 end } p fact      # {}: it starts off empty p fact[4]   # 24: 4! is 24 p fact      # {1=>1, 2=>2, 3=>6, 4=>24}: the hash now has entries   Related examples in the same category 1.  Creating Hashes 2.  You can test to see if a hash is empty with empty? 3.  Test how big it is with length or size 4.  use new to create a hash with a default value which is otherwise just nil 5.  access any key in a hash that has a default value 6.  Hash with => 7.  Hash.new with block logic

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