From: Joel VanderWerf <vjoel@...>
Date: 2001-09-01T10:30:10+09:00
Subject: [ruby-talk:20652] Re: Iterating by links

David Alan Black wrote:

> I'm still playing around with this :-)  but one possible source of
> problems is that you use a boolean test to end the series... which
> means, for example, that if you change this:
> 
>> tree = [[0, [1, 2]], 3, [4, 5, [6]]]
> 
> to this:
> 
>   tree = [[0, [1, 2]], 3, [4, 5, [6,7,nil]]]
> 
> it will not process tree[2][2][2].

Hi, David,

Good point. Maybe it should automatically check for respond_to? before 
sending the message. You can do that manually:

tree = [[0, [1, 2]], 3, [4, 5, [6, 7, nil]]]
for node in tree.by { |x| x.respond_to?(:at) && x.at(2) }
  p node
end

To handle this automatically, maybe catching an exception is faster 
than checking for respond_to? How about this change:

    def each
      cur = @first
      if @next_name
        begin
          loop do
            break unless cur
            yield cur
            cur = cur.send @next_name, *@args
          end
        rescue NameError
        end
      elsif @next_proc
    ....

Although I wouldn't want to do this without checking somehow that the 
exception was generated by the send in this method, rather than something 
called as a result of the send operation.

Failing that, we could put respond_to? inside the loop. I'll do some 
benchmarks to see if that's too bad.

Joel