From: Robert Klemme <shortcutter@...>
Date: 2006-11-15T17:45:05+09:00
Subject: Re: Design problem with 'inject'

On 15.11.2006 07:50, Marcel Molina Jr. wrote:
> On Wed, Nov 15, 2006 at 03:46:44PM +0900, Gary Boone wrote:
>> Ruby's inject has a design that can lead to hard to find bugs. The 
>> problem is that you don't have to specify what is summed; the value of 
>> the block is summed. That means 'next' can lead to a bug. Here's an 
>> example:
>>
>> No problem:
>>
>>    arr.inject(0) do |sum, i|
>>                     sum += i
>>                  done
>>
>> But suppose you need to skip some elements, so you add a 'next' 
>> statement.
>> Problem:
>>
>>    arr.inject(0) do |sum, i|
>>                    next if (i==3)
>>                    sum += i
>>                  done
> 
> You need to do this:
> 
>   next sum if i == 3
> 
> Also:
> 
>   sum += 1 
> 
> This unecessarily modifies the sum. 
> 
>   sum + 1
> 
> Will suffice.
> 
> marcel

In this case I would not even resort to #next.  This seems much more 
straightforward:

arr.inject(0) {|sum, i| i == 3 ? sum : sum + i}

or, if you do not like the ternary operator

arr.inject(0) {|sum, i| if i == 3 then sum else sum + i end}

IMHO #next is best used if the block is /long/ and you want to short 
circuit to the next iteration.  If it is a short block like in this case 
#next does not bring any benefits and in fact makes it more complicated 
to understand - at least in my opinion.

Kind regards

	robert