17

I'm currently using Sidekiq in a project and I have the following YAML config file:

:concurrency: 5
:pidfile: /tmp/pids/sidekiq.pid
:logfile: log/sidekiq.log
staging:
  :concurrency: 10
production:
  :concurrency: 20
queues:
  - default

I haven't seen having a colon in front of a key before but omitting that colon produces interesting results. In the case of the :pidfile: for example, with the colon in front it creates/overrides the destination file where is without it, it uses the one already there and does not write to it.

Is this documented somewhere or is this simply how Sidekiq expects certain keys?

Maikon
  • 1,382
  • 16
  • 16

2 Answers2

19

YAML keys starting with a colon are transformed into symbolized keys in Ruby when parsed, whereas keys without a colon will result in stringified keys:

require 'yaml'

string =<<-END_OF_YAML
:concurrency: 5
:pidfile: /tmp/pids/sidekiq.pid
:logfile: log/sidekiq.log
staging:
  :concurrency: 10
production:
  :concurrency: 20
queues:
  - default
END_OF_YAML

YAML.load(string)
# {
#     :concurrency => 5,
#     :pidfile     => "/tmp/pids/sidekiq.pid",
#     :logfile     => "log/sidekiq.log",
#     "staging"    => {
#         :concurrency => 10
#     },
#     "production" => {
#         :concurrency => 20
#     },
#     "queues"     => [
#         [0] "default"
#     ]
# }

Note: When a gem depends on symbolized keys, then a stringified key will not override its defaults.

spickermann
  • 100,941
  • 9
  • 101
  • 131
  • Plus one for symbolized keys. I've never seen that in Ruby before either, but have seen places where a symbol is required as a key. Good to know – TheJKFever Jul 29 '15 at 05:32
  • 1
    I understand how this behaves in Ruby here...but as far as syntactic YAML goes, is it legitimate to start a key with the colon, and it's just the Ruby interpreter that generates symbols out of keys that start with a colon? – Brian May 13 '16 at 18:25
5

It is actually not sidekiq specific. The colon in front of a key just makes this key a symbol instead of a string:

# example.yml
a:
  value: 1
:b:
  value: 2


yaml = YAML.load_file('example.yml')

yaml["a"] => { "value" => 1 }
yaml[:b] => { "value" => 1 }

So if your code accesses the config with key symbols, you should either add a colon in front of the key in the yaml file, or use some conversion of keys like #with_indifferent_access for the result hash (after parsing the yaml file)

Yury Lebedev
  • 3,985
  • 19
  • 26