% ruby --version
ruby 2.5.0dev (2017-11-18 trunk 60833) [x86_64-darwin15]
% ruby timer_test.rb
Traceback (most recent call last):
3: from t_test.rb:16:in `<main>'
2: from /Users/repeatedly/.rbenv/versions/2.5.0-dev/lib/ruby/gems/2.5.0/gems/cool.io-1.5.1/lib/cool.io/loop.rb:88:in `run'
1: from /Users/repeatedly/.rbenv/versions/2.5.0-dev/lib/ruby/gems/2.5.0/gems/cool.io-1.5.1/lib/cool.io/loop.rb:88:in `run_once'
t_test.rb:8:in `on_timer': wrong number of arguments (given 8, expected 0) (ArgumentError)
% ruby --version
ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin15]
% ruby timer_test.rb
:foo
:foo
:foo
...