ruby - Hash.fetch(not_exist_key) raises IndexError instead of KeyError -

in docs, says:

fetch(key [, default] ) → obj ; fetch(key) {| key | block } → obj

returns value hash given key. if key can’t found, there several options: no other arguments, raise keyerror exception; if default given, returned; if optional code block specified, run , result returned.

in terminal, irb says:

irb(main):001:0> hash = { 1 => "no one", 2 => "gonna", 3 => "fetch me" } => {1=>"no one", 2=>"gonna", 3=>"fetch me"}  irb(main):002:0> hash.fetch(4) indexerror: key not found     (irb):2:in `fetch'     (irb):2     :0 

can me explain that?

seems using older version of ruby. according 1.8.7 docs raises indexerror:

returns value hash given key. if key can’t found, there several options: no other arguments, raise indexerror exception; if default given, returned; if optional code block specified, run , result returned.

note keyerror subclass of indexerror in ruby 1.9+, rescuing indexerror works, too.