From: Eleanor McHugh <eleanor@...>
Date: 2008-05-28T21:48:20+09:00
Subject: Re: The duck's backside

On 28 May 2008, at 11:01, Tobias Weber wrote:
> def doit(a, b, c = nil)
>  begin
>    if c.nil? and b > 0
>      c = "ignore"
>    elsif b.nil? and c > 0
>      uaid = "ignore"
>    else
>      raise
>    end
>  rescue RuntimeError, NoMethodError
>    raise ArgumentError, "need exactly one number"
>  end
>  @http.post("first=#{a}&second=#{b}&third=#{c}")
> end


This is off the top of my head so the usual caveats apply:

	def doit a, b, c = nil
		begin
			case
			when b && c
				raise
			when b && b.respond_to?(:to_int)
				uaid = "ignore" if b.to_int > 0
			when c && c.respond_to?(:to_int)
				c = "ignore" if c.to_int > 0
			else
				raise
			end
		rescue
			raise ArgumentError, "need exactly one number"
		end
		@post("first=#{a}&second=#{b.to_int}&third=#{c.to_int}")
	end

This makes the exclusion of b and c more explicit, which will make it  
much easier for a maintainer to understand what's going on. I've also  
made integer conversion explicit and focused the filtering logic on  
making sure it's appropriate as that's what you're really trying to  
achieve, however this kind of belt-and-braces approach suggests that  
you're tackling the problem from the wrong angle and should look at  
the data-flow elsewhere in your code.

One possibility would be to rejig the whole thing as follows:

	def doit a, v, param = :second
		raise ArgumentError, "needs a numeric value" unless v.respond_to? 
(:to_int)
		v = "ignore" if (param == :third) && v > 0
		@post("first=#{a}&second=#{v if param == :second}&third=#{v if param  
== :third}")
	end

and then evolve it from there, although it's also pretty damn ugly.

Where this is called you could write something along the lines of:

	if b && c then
		raise ArgumentError, "needs exactly one additional argument"
	else
		doit a, (b || c), (b.nil? ? :third : :second)
	end

which could be further encapsulated as:

	doit a, b, c = nil
		raise ArgumentError, "needs exactly one additional argument" if b && c
		v = b || c
		raise ArgumentError, "need a numeric parameter" unless v.respond_to? 
(:to_int)
		param = b.nil? ? :third : :second
		v = "ignore" if (param == :third) && v > 0
		@post("first=#{a}&second=#{v if param == :second}&third=#{v if param  
== :third}")
	end


Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net
----
raise ArgumentError unless @reality.responds_to? :reason