From: "yermej@..." <yermej@...>
Date: 2007-10-18T04:55:03+09:00
Subject: Re: How to combine blocks and recursiveness

On Oct 17, 12:36 pm, Luis <lcres...@gmail.com> wrote:
> Hello,
>
> I am trying to code a method that accepts a block... easy. The problem
> is that this method is recursive, so I don't know how to pass the
> block through the recursive calls.
>
> The specific code is about recurising through a directory tree while
> calling the provided code block once per each directory, passing the
> list of files in that directory. This is the code:
>
> class DirInfo
>
>         # constructor, etc. removed for clarity
>
>         def scan
>                 @path.each_entry do |p|
>                         next if p.to_s == "." || p.to_s == ".."
>                         p = @path + p
>                         if p.file?
>                                 finf = FileInfo.new(p)
>                                 @files << finf
>                         elsif p.directory?
>                                 dinf = DirInfo.new(p)
>                                 dinf.scan       # ==> Recursive search of subdirs
>                         end
>                 end
>                 yield @path, @files
>         end
>
> end
>
> So if I do:
>
> di = DirInfo.new("/devtools/ruby")
> di.scan do |path, files|
>         puts "Directory #{path} has #{files.length} files"
> end
>
> I expect to get my block called once per each subdirectory, passing
> the subdir path and list of files in that subdir. The problem is that
> the fisrt time the call scan is made from within scan, no block is
> given, so I get a "no block given" exception and the program stops.
>
> I know there are other ways to scan directories, but please take it
> just as an example. Still the question is, how to combine
> recursiveness with blocks?
>
> Thanks in advance,
>
>    Luis.

You can make the block argument explicit:

def scan(&block)
  # do stuff
  scan &block  # <== recursive call with block
  yield
end

I think that'll work.