From: Brian Candler <b.candler@...>
Date: 2010-08-04T17:12:51+09:00
Subject: Re: Remove the error

Amir Ebrahimifard wrote:
> Hi
> Why these codes result error ?
> 
> 1-
> array = [*1..10]
> sum = array.inject { |memo,item| memo+item if item !=3 }

sum = array.inject(0) { |memo,item| item != 3 ? memo+item : memo }

Note a subtlety here: if you omit the (0) argument then the initial memo 
is always set to the first item, so you wouldn't be able to skip it.

>> array.inject { |memo,item| item != 1 ? memo+item : memo }
=> 55
>> array.inject(0) { |memo,item| item != 1 ? memo+item : memo }
=> 54

> 2-
> array = [*1..10]
> sum = array.inject { |memo,item| puts memo+item }

sum = array.inject { |memo,item| puts memo,item; memo+item }

In both cases, you need to ensure that the last expression evaluated by 
the block is the value you want for the 'memo' in the next iteration.
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