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