From: Michael Neumann <neumann@...>
Date: 2001-09-02T00:44:59+09:00
Subject: [ruby-talk:20672] Re: corresponding "non-bang" method to []=

Tobias Reif wrote:
> Hi,

Hi,

> There's "collect", and the bang version "collect!"
> 
> AFAICS, []= is bang. What's the non-bang version?

There's no one.
Does it make sense to have one? Not for me.
You may copy the receiver before with dup or clone, like Python's does with [:] when
changing an array inside a for-loop.

> I'm trying to modify specific members of an array, depending on their 
> position in the array ("second and last get a newline" etc.).

> I'm working my way through the docs, faqs, and the Pickaxe.
> Now after hours of trying, I only got it to work using a dirty hack.
> I'm looking for a nice way.
> 
> So because in collect there is no index passed to the block, I need to 
> use each_index, where I need to use []= to set the new value. (AFAIK)
> 
> But I don't want to modify the original, because I need to modify it 
> differently in another method starting from it's previous state.
> 
> In pseudo-code:
> 
> an_array.each_index do |x|
>   new_val = an_array.at(x) + "\n"
>   if (x == 2) or (x == (an_array.size - 1))
>    an_array.set_at(x,new_val)
>   end
> end

  an_array.dup.each_index do |x|
     ...
  end

should do it.

> or
> 
> an_array.collect |index,item|
>    if (index == 2) or (index == (an_array.size - 1))
>      item + "\n"
>    else
>      item
>    end
> end

How about:

  an_array[0..1]  + [an_array[2]  + "\n"] + 
  an_array[3..-2] + [an_array[-1] + "\n"] 

Alternatively, you may use a counter:

  index = -1
  an_array.collect do |item|
     index += 1
     if (index == 2) or (index == (an_array.size - 1))
       item + "\n"
     else
       item
     end
  end

or otherwise create an array that contains subarrays with "index,item" as elements:

  an_array.collect {|i| [nil, i]}.each_with_index{|i, e| e[0] = i}.collect do |index, item|
    ... proceed as above
  end


Regards,

  Michael

-- 
Michael Neumann
merlin.zwo InfoDesign GmbH
http://www.merlin-zwo.de