From: dblack@...
Date: 2007-01-08T21:37:05+09:00
Subject: Re: a most undangerous Hash#store!

Hi --

On Mon, 8 Jan 2007, Mauricio Fernandez wrote:

> On Mon, Jan 08, 2007 at 08:20:05PM +0900, Robert Klemme wrote:
>> On 08.01.2007 02:59, dblack@wobblini.net wrote:
>>> On Mon, 8 Jan 2007, Florian Gross wrote:
>>>> On 2007-01-08 02:00:10 +0100, dblack@wobblini.net said:
>>>>
>>>>> hsh[:key] = "value" unless hsh.has_key? :key
>>>>> You can use merge and a one-key hash:
>>>>>
>>>>>   hash.merge({ :key => "new value" })
>>>>
>>>> Hm, not really:
>>>>
>>>> { :key => "old value" }.merge({ :key => "new value" }) # =>
>>>> {:key=>"new value"}
>>>
>>> True -- that's a bit of a deal-breaker :-)
>>
>> But only if you need the return value:
>>
>> irb(main):001:0> hash={:key=>1}
>> => {:key=>1}
>> irb(main):002:0> hash.merge( :key => "new value" )
>> => {:key=>"new value"}
>> irb(main):003:0> hash
>> => {:key=>1}
>>
>> The hash is merged properly.
>
> The original hash is not modified by #merge.
> #merge != #merge! (== #update)
>
> a = {}
> a.merge(:foo => 1)        # => {:foo=>1}
> a                         # => {}

Yes, merge was just a wrong turn on my part.  Forget it.


David

-- 
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