Ruby/Array/to Hash

class Array
  def to_h(default=nil)
    Hash[ *inject([]) { |a, value| a.push value, default || yield(value) } ]
  end
end
a = [1, 2, 3]
a.to_h(true)
# => {1=>true, 2=>true, 3=>true}
a.to_h { |value| [value * -1, value * 2] }
# => {1=>[-1, 2], 2=>[-2, 4], 3=>[-3, 6]}