From: Brian Candler <b.candler@...>
Date: 2010-09-17T03:56:14+09:00
Subject: Re: Traversing a friend graph - the ruby way?

Alex Stahl wrote:
> Recently, I needed to write some code to traverse friend graphs on my
> website.  Due to my C++ background, I used recursion:
> 
> def traverse(user, depth, origin=nil)
>   @hi5 = Hi5fbapi.new @api_key, @secret
>   if depth > 0
>     friends = @hi5.get_friends(user)
>     friends.delete origin if friends.include? origin
>     depth -= 1
>     friends.each do |friend|
>       traverse(friend, depth, user)
>     end
>   end
> end
> 
> But as I continue to learn the finer points of ruby, I can't help but
> think there's a more ruby-oriented way to do this.  Any suggestions?

That's a perfectly good way to traverse a graph. I'd just say: don't use 
an instance variable (@hi5), use a local variable (hi5) instead.

There is only a single instance variable for your object, so when you 
recurse and assign to @hi5, you are stomping on the value set in the 
caller. In this particular example it doesn't matter, but in other 
algorithms it would.

Or: if a single Hi5fbapi object could be used by all levels, then just 
create one before you start recursing, and then pass it to a recursive 
helper method.

def traverse(..)
  hi5 = Hi5fbapi.new @api_key, @secret
  do_traverse(hi5, ...)
end

def do_traverse(hi5, ...)
  ..
  do_traverse(hi5, ...)
  ..
end
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