From: bertrandmuscle@...
Date: 2005-03-28T08:34:47+09:00
Subject: Re: ! haphazard

Florian Frank wrote:
> Daniel Amelang wrote:
> 
>> Gotcha. Well, I can tell you firsthand about the controversies of the
>> 'bang' methods (like 'sort!', etc). Since they really aren't a
>> necessity (you can get along with just the non-bang versions) and ruby
>> has only relatively recently acquired sort_by, I bet they just didn't
>> get around to writing the bang version of sort_by.
>>  
>>
> sort! sorts an array in place, while sort always makes a copy from the 
> original array. This distinction wouldn't be sensible for sort_by, 
> because it's actually a Schwartzian Transform, that always creates 
> temporary arrays:
> 
> class Array
>  def sort_by
>    map { |x| [ x, yield(x) ] }.sort { |a,b|
>      a.last <=> b.last
>    }.map { |p| p.first }
>  end
> end
> 
> The transform makes a lot of sense if the yielded computations is very 
> expensive, because O(n) < O(n*log(n)). It's good to know about the trade 
> off between creating temporary arrays and the computation of the sort 
> keys, if one has to choose between sort(!) and sort_by.
> 

this is very interesting, thank you.

but for myself and perhaps many other users it comes down to how 
intuitive the language is. from this perspective: if sort! works, 
sort_by! should also.

one of the things that drew me to ruby recently was this philosophy, but 
there have been some off-putting inconsistencies.