From: Alex Fort <imphasing@...>
Date: 2010-06-15T23:41:12+09:00
Subject: Re: Unexpected behavior in inject

On Tue, Jun 15, 2010 at 10:31 AM, Jonathan Nielsen <jonathan@jmnet.us> wrote:
>> [1,2,3].inject(0) do |acc, num|
>>  acc + num
>>  puts acc
>> end
>>
>>
>> Ruby gives me this error:
>>
>> bash ~ $ ruby test.rb
>> 0
>> test.rb:2: undefined method `+' for nil:NilClass (NoMethodError)
>>        from test.rb:5:in `inject'
>>        from test.rb:1:in `each'
>>        from test.rb:1:in `inject'
>>        from test.rb:1
>>
>> This seems pretty strange to me, as if puts is modifying the accumulator by
>> resetting it to nil. Is this normal behavior? If so, I would greatly
>> appreciate it if someone could point me in the right direction as to why
>> this is the way it is.
>
>
> Yes, this is exactly as expected.  The last statement you put in the block
> is the return value of the block.  'puts' always returns nil, so the next
> iteration acc is nil.
>
> To get the behavior you are looking for:
>
> [1,2,3].inject(0) do |acc, num|
>  sum = acc + num
>  puts sum
>  sum
> end
>
> Now since 'sum' is the final statement in the block, acc will be sum for the
> next iteration.

I understand now. Thank you for clarifying that for me.


Alex