From: Roy Zuo <roylzuo@...>
Date: 2011-04-25T21:18:48+09:00
Subject: Re: problem with ruby19's Hash behavior

Hi,

I still cannot understand. 

In the first example, result[:mem] should be [ ] before "result[:mem] << i" is
executed. Afterwards it should be [1], and the return value should be {:mem =>
[1]}. 

In the second example, what does "<<=" stand for?

Roy

On Mon, Apr 25, 2011 at 08:50:13PM +0900, Roger Braun wrote:
> Hi Aaron
> 
> 2011/4/25 Aaron <aaron2ti@gmail.com>:
> > see the following codes pls, I wonder if this's a intent or a bug. For me the first line sounds better having same result with the later line
> >
> >>> [1].inject(Hash.new {[]}){ |result, i| result[:mem] << i;   result }
> > => {}
> >>> [1].inject(Hash.new {[]}){ |result, i| result[:mem] <<= i; result }
> > => {:mem=>[1]}
> 
> It's the expected behaviour. See
> http://ruby-doc.org/core/classes/Hash.html#M000718.
> 
> "If a block is specified, it will be called with the hash object and
> the key, and should return the default value. It is the block‘s
> responsibility to store the value in the hash if required."
> 
> [1].inject(Hash.new {|h,k| h[k] = Array.new}){ |result, i|
> result[:mem] << i;   result }
>  => {:mem=>[1]}
> 
> -- 
> Roger Braun
> rbraun.net | humoralpathologie.de
> 

--