From: mike@... (Mike Stok)
Date: 2003-08-12T22:43:49+09:00
Subject: Re: hash default value

In article <3F38FA17.1080008@wanadoo.fr>,
Emmanuel Touzery  <emmanuel.touzery@wanadoo.fr> wrote:
>Hello,
>
>    I'm bitten by a hash default value problem. I wanted to avoid the
>myHash[a] = {} if !myHash[a]; myHash[a]["blue"] = 1
>    pattern by using hash default values, but i get an unexpected (for 
>me) result:
>
>irb(main):001:0> myHash = {}
>{}
>irb(main):002:0> myHash["blue"]["red"] = 1
>NameError: undefined method `[]=' for nil
>        from (irb):2
>irb(main):003:0> myOtherHash = Hash.new({})
>{}
>irb(main):004:0> myOtherHash["blue"]["red"] = 1
>1
>irb(main):005:0> p myOtherHash
>{}
>nil
>
>i expected that myOtherHash would be {"blue"=>{"red"=>1}}
>
>what am i missing here? is there a workaround to the ugly syntax i said 
>i want to avoid? (you have the right to say "store your data in a decent 
>manner")

In recent rubys (I tried on 1.8) you can say

  myHash = Hash.new { |h, k| h[k] = Hash.new }

so that the newly created sub-hash is installed in the original hash.

This behaves as you want...

>> myHash['blue']['red'] = 1
=> 1
>> myHash['blue']['green'] = 2
=> 2
>>  myHash['crimson']['king'] = 69
=> 69
>> p myHash
{"crimson"=>{"king"=>69}, "blue"=>{"green"=>2, "red"=>1}}

Hope this helps,

Mike
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