Colon in the front: YAML syntax

Question

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
st         


        

Answer 1

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)

Answer 2

YAML keys starting with a colon generate symbolized keys in Ruby, whereas keys without a colon will generate 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: If a gem depends on symbolized keys then the stringified keys will not override its defaults.