Rubyのunlessってなんのメリットあるん。
だって全部別にifでええやん。
irb(main):006:0* grades = { "Jane Doe" => 10, "Jim Doe" => 6 }
=> {"Jane Doe"=>10, "Jim Doe"=>6}
irb(main):011:0> "Bingo!" unless grades.has_key?('Jim Doada')
=> "Bingo!"
irb(main):015:0* "Bingo!" unless grades.has_key?('Jim Doe')
=> nil