Given the following method that takes one argument:
def foo(arg); p arg; end
I can call it with an empty array:
foo([])
# prints []
I can also save it as a Method object and call that with an empty array, with the same result:
method(:foo).call([])
# prints []
However, if I convert the Method object to a Proc and call that with an empty array, I get an ArgumentError:
method(:foo).to_proc.call([])
# ArgumentError: wrong number of arguments (0 for 1)
# from (irb):4:in `foo'
# from (irb):4:in `to_proc'
# from (irb):10:in `call'
I expected it to behave the same as the previous two cases. Instead, it seems to be behaving as if I'd written foo(*[]). However, if I call it with a non-empty array, it does behave the way I expected:
method(:foo).to_proc.call([1])
# prints [1]
So it destructures the argument, but only if the argument happens to be an empty array. And only if I call Method#to_proc.
Is there a gap in my understanding of how Method or Proc work, or is this a bug?
I'm running Ruby 1.8.7-p299. I observe the same behaviour in 1.8.6-p399 and 1.8.7-head. However, I don't see it in 1.9.1-p378: there all three forms print [] when called with an empty array.