Configuration options for nit tools and apps

This module provides basic services for options handling in your Nit programs.

Basic configuration holder

The Config class can be used as a simple option holder and processor:

import config

# Create a new config option
var opt_my = new OptionString("My option", "--my")

# Create the config and add the option
var config = new Config
config.add_option(opt_my)

# Parse the program arguments, usually `args`
config.parse_options(["--my", "myOption", "arg1", "arg2"])

# Access the options and args
assert opt_my.value == "myOption"
assert config.args == ["arg1", "arg2"]

Custom configuration class

Instead of using basic Config instances, it is better to define new sublcasses to store options and define custom services.

import config

class MyConfig
    super Config

    var opt_my = new OptionString("My option", "--my")

    init do
        super
        tool_description = "Usage: MyExample [OPTION]... [ARGS]..."
        add_option(opt_my)
    end

    fun my: String do return opt_my.value or else "Default value"
end

var config = new MyConfig
config.parse_options(["--my", "myOption", "arg1", "arg2"])

assert config.my == "myOption"
assert config.args == ["arg1", "arg2"]

We define the my method to provide an elegant shortcut to opt_my.value and define the default value if the option was not set by the user.

The tool_description attribute is used to set the usage header printed when the user request the help message.

config.parse_options(["-h"])
if config.help then
    config.usage
    exit 0
end

This will display the tool usage like this:

Usage: MyExample [OPTION]... [ARGS]...
 -h, --help   Show this help message
 --my         My option

Configuration with ini file

The IniConfig class extends Config to add an easy way to link your configuration to an ini file.

class MyIniConfig
    super IniConfig

    var opt_my = new OptionString("My option", "--my")

    init do
        super
        tool_description = "Usage: MyExample [OPTION]... [ARGS]..."
        opts.add_option(opt_my)
    end

    fun my: String do return opt_my.value or else ini["my"] or else "Default"
end

This time, we define the my method to return the option value or the ini if no option was passed. Finally, if no ini value can be found, we return the default value.

By default, IniConfig looks at a config.ini file in the execution directory. This can be overrided in multiple ways.

First by the app user by setting the --config option:

var config = new MyIniConfig
config.parse_options(["--config", "my_config.ini"])

assert config.config_file == "my_config.ini"

Default config file can also be changed by the library client through the default_config_file attribute:

config = new MyIniConfig
config.default_config_file = "my_config.ini"
config.parse_options(["arg"])

assert config.config_file == "my_config.ini"

Or by the library developper in the custom config class:

class MyCustomIniConfig
    super IniConfig

    redef var default_config_file = "my_config.ini"
end

var config = new MyCustomIniConfig
config.parse_options(["arg"])

assert config.config_file == "my_config.ini"