Default Value support #67

parser.on('-m', '--tracing-mode MODE', 'Define the category of events traced', default: 'default')

require 'optparse'
class OptionParserWithDefaultAndValidation < OptionParser
  def initialize
    # Dictionary to save the default values passed by `on`
    @defaults = {}
    super
  end

  def parse!(argv = default_argv, into: nil)
    # Merge the default value with the `into` dict
    into.merge!(@defaults) unless into.nil?
    # This will populate the `into` dict (overwriting our default if needed)
    super
  end

  def define(*opts, &block)
    switch = super
    @defaults[switch.switch_name] = @tmp_default unless @tmp_default.nil?
    switch
  end

  def on(*opts, default, &block)
    # Save the default, which will be used in `refine.`
    @tmp_default = default
    # Default can contain Array (or Set).
    # We cannot use the [a].flatten trick.
    # So we use the respond_to one
    #   irb(main):028:0> default = Set[-1,2]
    #   => #<Set: {-1, 2}>
    #   irb(main):029:0> [default].flatten.join(',')
    #   => "#<Set: {-1, 2}>"
    #   irb(main):030:0> default.respond_to?(:flatten)? default.flatten.join(',') : default
    #   => "-1,2"
    opts << "Default: #{default.respond_to?(:flatten) ? default.flatten.join(',') : default}" unless default.nil?
    super(*opts, &block)
  end
end