Extension for Ruby's Hash class: - `Hash#replace_key!` - `Hash#replace_key`

replace_key.rb

class Hash
  def replace_key!(a, b)
    if self[a]
      self[b] = self.delete(a)
    end

    self
  end

  def replace_key(a, b)
    if self[a]
      self.dup.replace_key!(a, b)
    else
      self
    end
  end
end