From: David Alan Black <dblack@...>
Date: 2002-03-31T11:20:45+09:00
Subject: Re: Array#join accept a codeblock?

Hello --

On Fri, 29 Mar 2002, Tom Robinson wrote:

> Is there some way to do something like Array#join that takes a
> codeblock to tell it what to join up the array with?  Something
> like...
>
> ary = [1,2,3,4,5]
> str = ary.myjoin { |idx|
>   if idx == 1
>     ' ** '
>   else
>     ' -- '
>   end
> }
>
> gives str as "1 -- 2 ** 3 -- 4 -- 5"
>
> I have written something like this below, but I was wondering if
> there's anything like this in ruby, or if not maybe it could be added
> to the next version. :)
>
> class Array
>   def myjoin
>     outstr = ""
>     self.each_index { |idx|
>       if idx == self.length - 1
>         outstr += self[idx].to_s
>       else
>         outstr += self[idx].to_s + yield(idx).to_s
>       end
>     }
>     return outstr
>   end
> end
>
> I'm new to ruby so critiques on this code would be useful.

Just some stylistic playing around (haven't benchmarked or anything)....

Going for the minimalist, no temporary variables look, I came up with:

  def myjoin
    [(0...size-1).map {|i| at(i).to_s + yield(i).to_s}, at(-1).to_s].join
  end

And, a somewhat kindler, gentler verion (restoring the temp variable):

  def myjoin
    res = ""
    (0...size-1).each {|i| res += at(i).to_s + yield(i).to_s}
    res << at(-1).to_s
  end

If you want to use this as #join, and without breaking old code, you
can do:

  class Array
    alias :oldjoin :join
    def myjoin(sep=$,)
      if block_given?
	res = ""
	(0...size-1).each {|i| res += at(i).to_s + yield(i).to_s}
	res << at(-1).to_s
      else
	oldjoin(sep)
      end
    end
  end

(Also means you don't have to worry about having it added to the
core language :-)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav