From: "Bartosz Dziewoński" <matma.rex@...>
Date: 2012-08-06T03:19:20+09:00
Subject: Re: Redefining constants for a given instance only

Sooo... how badly do you need this? Because if the answer is "very
badly", then you could do this:

(If someone asks, I didn't recommend this. The code that follows is
braindead, wrong on multiple levels, and *will* fail in unpredictable
ways in production. You have been warned.)

	class ClassA
	end

	class ClassB
	end

	class Evaluator
		def evaluate
			# to make the source more interesting
			if true
				return ClassA
			else
				return nil
			end
		end
	end

	ev = Evaluator.new
	ev2 = Evaluator.new

	file, line = ev.method(:evaluate).source_location
	lines = File.readlines(file)
	indent = lines[line-1][/^\s*/]
	source_lines = lines.drop(line).take_while{|ln| ln=~/#{indent}\s/o  }
	source = lines[line-1] + source_lines.join("\n") + "end\n"

	# this could be done better, but anything reasonable involving
singleton_class failed on me
	eval "class<<ev; " + source.gsub('ClassA', 'ClassB') + "; end"

	puts ev.evaluate #=> ClassB
	puts ev2.evaluate #=> ClassA



-- Matma Rex