Question

Im trying to do some metaprogramming and would like to know the names of the variables passed as block arguments:

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?

Answer 1

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.