ruby-192-flatten-bug.rb

# Array#flatten seems to call #to_ary on all elements of the array, regardless 
# of whether they are Arrays and without checking if the object has a to_ary first.
#
# More peculiarly, calling "super" inside of method_missing does not return from
# the call to the method_missing method, instead it jumps completely out of
# the call without performing any actions after "super" is called. 
#
# Note that Foo.new.respond_to?(:to_ary) == false, so method_missing should raise an
# exception, though it does not.

class Foo
  def method_missing(meth, *args, &block)
    puts "calling method: #{meth}"
    p super
    puts "AFTER SUPER"
  end
end

[Foo.new].flatten
puts "END"

# Expected (assuming super does not raise exception, though it should):
# 
# calling method: to_ary
# <<some value, nil maybe>>
# AFTER SUPER
# END
# 
# Actual:
# 
# calling method: to_ary
# END
#