From: Robert Klemme <shortcutter@...>
Date: 2009-08-19T00:14:51+09:00
Subject: Re: How can I extract variables from a ruby snippet

2009/8/18 Brian Candler <b.candler@pobox.com>:
> Otherwise, you could execute the template using erb, and use
> method_missing to pick up attempts to access local variables. From these
> return a dummy object, which again uses method_missing to see what
> methods have been called on that dummy object. If the method_missing
> passes a block then you will need to yield the block with dummy
> arguments.

I toyed around a bit - this solution is by far not perfect!

#!ruby19 -w

class FillIn < Object
  def initialize(name)
    @name = name.to_s
  end

  def method_missing(s,*a,&b)
    a.map! {|x| x.inspect}

    nn = case s
    when :[]
      "#{@name}[#{a.join(', ')}]"
    when :[]=
      v = a.slice!(-1, 1)
      "#{@name}[#{a.join(', ')}]=#{v}"
    else
      if a.empty?
        "#{@name}.#{s}"
      else
        "#{@name}.#{s}(#{a.join(', ')})"
      end
    end

    puts nn
    self.class.new(nn)
  end

  def to_s
    @name
  end

  alias inspect to_s
end

root = FillIn.new "root"
p root

root.foo.bar['help'].length
root.foo.bar[FillIn.new("x")].length

> This may be good enough for what you need, but isn't guaranteed to catch
> all possible execution paths. e.g. what about
>
>  <% if foo %>
>    <%= foo.xxx %>
>  <% else %>
>    <%= bar.yyy %>
>  <% end %>
> ?
>
> You are going to find it hard to exercise both branches of this
> conditional. Similarly with loops, where the nth iteration may behave
> differently to the previous ones.

Correct.  I feel somehow reminded of
http://en.wikipedia.org/wiki/Halting_problem :-)

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/