Mixlib::Config
¶ ↑
Mixlib::Config
provides a class-based configuration object, as used in Chef. To use in your project:
require 'mixlib/config' module MyConfig extend Mixlib::Config config_strict_mode true default :first_value, 'something' default :other_value, 'something_else' end
You can use this to provide a configuration file for a user. For example, if you do this:
MyConfig.from_file('~/.myconfig.rb')
A user could write a Ruby config file that looked like this:
first_value 'hi' second_value "#{first_value}! 10 times 10 is #{10*10}!"
Inside your app, you can check configuration values with this syntax:
MyConfig.first_value # returns 'something' MyConfig[:first_value] # returns 'something'
And you can modify configuration values with this syntax:
MyConfig.first_value('foobar') # sets first_value to 'foobar' MyConfig.first_value = 'foobar' # sets first_value to 'foobar' MyConfig[:first_value] = 'foobar' # sets first_value to 'foobar'
Nested Configuration¶ ↑
Often you want to be able to group configuration options to provide a common context. Mixlib::Config
supports this thus:
require 'mixlib/config' module MyConfig extend Mixlib::Config config_context :logging do default :base_filename, 'mylog' default :max_log_files, 10 end end
The user can write their config file in one of three formats:
Method Style¶ ↑
logging.base_filename 'superlog' logging.max_log_files 2
Block Style¶ ↑
Using this format the block is executed in the context, so all configurables on that context is directly accessible
logging do base_filename 'superlog' max_log_files 2 end
Block with Argument Style¶ ↑
Using this format the context is given to the block as an argument
logging do |l| l.base_filename = 'superlog' l.max_log_files = 2 end
You can access these variables thus:
MyConfig.logging.base_filename MyConfig[:logging][:max_log_files]
Default Values¶ ↑
Mixlib::Config
has a powerful default value facility. In addition to being able to specify explicit default values, you can even specify Ruby code blocks that will run if the config value is not set. This can allow you to build options whose values are based on other options.
require 'mixlib/config' module MyConfig extend Mixlib::Config config_strict_mode true default :verbosity, 1 default(:print_network_requests) { verbosity >= 2 } default(:print_ridiculously_unimportant_stuff) { verbosity >= 10 } end
This allows the user to quickly specify a number of values with one default, while still allowing them to override anything:
verbosity 5 print_network_requests false
Strict Mode¶ ↑
Misspellings are a common configuration problem, and Mixlib::Config
has an answer: config_strict_mode
. Setting config_strict_mode
to true
will cause any misspelled or incorrect configuration option references to throw Mixlib::Config::UnknownConfigOptionError
.
require 'mixlib/config' module MyConfig extend Mixlib::Config config_strict_mode true default :filename, '~/output.txt' configurable :server_url # configurable declares an option with no default value config_context :logging do default :base_name, 'log' default :max_files, 20 end end
Now if a user types fielname "~/output-mine.txt"
in their configuration file, it will toss an exception telling them that the option “fielname” is unknown. If you do not set config_strict_mode, the fielname option will be merrily set and the application just won’t know about it.
Different config_contexts can have different strict modes; but they inherit the strict mode of their parent if you don’t explicitly set it. So setting it once at the top level is sufficient. In the above example, logging.base_naem 'mylog'
will raise an error.
In conclusion: always set config_strict_mode to true. You know you want to.
Testing and Reset¶ ↑
Testing your application with different sets of arguments can by simplified with reset
. Call MyConfig.reset
before each test and all configuration will be reset to its default value. There’s no need to explicitly unset all your options between each run.
NOTE: if you have arrays of arrays, or other deep nesting, we suggest you use code blocks to set up your default values (default(:option) { [ [ 1, 2 ], [ 3, 4 ] ] }
). Deep children will not always be reset to their default values.
Enjoy!