How can I find the names of argument variables passed to a block

Im trying to do some metaprogramming and would like to know the names of the variables passed as block a开发者_如何学Crguments:

z = 1 # this variable is still local to the block   

Proc.new { |x, y| local_variables }.call

# => ['_', 'z', x', 'y']

I am not quite sure how to differentiate between the variables defined outside the block and the block arguments in this list. Is there any other way to reflect this?

Here's how you can tell in Ruby 1.8:

>> z = 1
=> 1
>> Proc.new{|x| "z is #{defined? z}, x is #{defined? x}"}.call(1)
=> "z is local-variable, x is local-variable(in-block)"

but, caution! this doesn't work in Ruby 1.9 - you'll get

=> "z is local-variable, x is local-variable"

and I don't know the answer then.

As for a ruby 1.9 solution I am not 100% sure but ruby 1.9.2 is adding a Method#parameters method which returns the params in an array of :symbols

irb(main):001:0> def sample_method(a, b=0, *c, &d);end
=> nil
irb(main):002:0> self.method(:sample_method).parameters
=> [[:req, :a], [:opt, :b], [:rest, :c], [:block, :d]]

Not sure if they have a solution for block parameters as well.