From: Leslie Viljoen <leslieviljoen@...>
Date: 2009-10-27T00:32:50+09:00
Subject: Setting instance variables from hash parameters (with defaults)

Hi!

I'm sure I might be reinventing the wheel here.
I was writing the following ugly code in order to set options (with
defaults) from a hash:

	def initialize(opts = {})
		@select_max = opts.has_key?(:select_max) ? opts[:select_max] : 10000
		@select_try = opts.has_key?(:select_try) ? opts[:select_try] : 1000
		@min_sleep_sec = opts.has_key?(:min_sleep_sec) ? opts[:min_sleep_sec] : 5
		@max_sleep_sec = opts.has_key?(:max_sleep_sec) ? opts[:max_sleep_sec] : 1800
		@default_sleep = opts.has_key?(:default_sleep) ? opts[:default_sleep] : 10
....

So to avoid that I wrote:

module Defaulting
	def set_params(defs, params)
		defs.each do |name, val|
			if params.has_key?(name)
				eval "@#{name} = params[name]"
			else
				eval "@#{name} = val"
			end
		end
	end
end

So that I could do the much nicer:

	include Defaulting
	def initialize(opts = {})
		defs = {
			:select_max => 10000,
			:select_try => 1000,
			:min_sleep_sec => 5,
			:max_sleep_sec => 1800,
			:default_sleep => 10
		}
		set_params(defs, opts)

....

Note that this allows me to pass options that are explicitly set to nil.

Now:
1. Is this functionality already tucked away somewhere else?
2. How can I get rid of those nasty evals?