Hash#map_value, Hash#map_key, Hash#map_pair.

additional_hash_methods.rb

class Hash
  def map_value
    each_pair.with_object({}) do |(key, value), result|
      result[key] = yield value
    end
  end
  
  def map_key
    each_pair.with_object({}) do |(key, value), result|
      result[yield key] = value
    end
  end
  
  def map_pair &block
    Hash[map &block]
  end
end

hash = { aim: true }
#=> {:aim=>true}

hash.map_value &:to_s
#=> {:aim=>"true"}

hash.map_key &:to_s
#=> {"aim"=>true}

hash.map_pair { |k, v| [k.to_s, v.to_s] }
#=> {"aim"=>"true"}

# Thanks to heftig for the refactor!