From: Nikolai Weibull <now@...>
Date: 2007-11-16T07:24:05+09:00
Subject: Re: Thoughts about Array#compact!, Array#flatten!, Array#reject!, String#strip!, String#capitalize!, String#gsub!, etc.

On Nov 15, 2007 8:14 PM, Wolfgang N�dasi-Donner <ed.odanow@wonado.de> wrote:

> The methods listed in the header return "nil" when nothing was done. This may be
> usefull and used in several situations.
>
> Unfortunately there is possible usage of these methods, when this return value
> is a very bad thing: In a method-chain like...
>
> "I am a 20MB string".downcase.split(/\s+/).reject{|s|s.length>20}
>
> In this case the initial string, the result of "downcase", and of "split" will
> only be used once - they are single threaded. If, as the example text will name,
> the original String object is about 20MB, "downcase" will produce a copy, which
> will be thrown away. The same is true for "reject". It would be much better to
> use...
>
> "I am a 20MB string".downcase!.split(/\s+/).reject!{|s|s.length>20}
>
> ...but this is not possible, because "downcase!" and "reject!" will return "nil"
> if they have nothing to do.

Your problem isn't the return value of downcase!.  Your problem is a
String, 20MB in size.