keymaster.rb

class Wrapper
  attr_reader :string

  def initialize(string)
    @string = string
  end

  def upcase!
    string.upcase!
  end
end


hash = { Wrapper.new("apple") => "pie" }
# => {#<Wrapper:0x007fe2114fc388 @string="apple">=>"pie"}
hash.keys.each { |k| k.upcase! }
# => [#<Wrapper:0x007fe2114fc388 @string="APPLE">]
hash
# => {#<Wrapper:0x007fe2114fc388 @string="APPLE">=>"pie"}