From: Robert Klemme <bob.news@...>
Date: 2005-10-12T23:11:53+09:00
Subject: Re: Hash as a class variable

OliverMarchand wrote:
> Hi ruby fans,
>
> I am a python2ruby switcher and just encountered this problem today
> with a class variable:
>
> ---
> class Testclass
>   @@myhash = Hash.new({"a"=>"aaaah"})
>   def initialize()
>     p @@myhash
>   end
> end
> T = Testclass.new
> ---
> yields
> {}

>> class Testclass
>>   @@myhash = {"a"=>"aaaah"}
>>   def initialize()
>>     p @@myhash
>>   end
>> end
=> nil
>> T = Testclass.new
{"a"=>"aaaah"}
=> #<Testclass:0x10188fb0>

You are providing a default value to the hash:

>> h=Hash.new("foo")
=> {}
>> h[1]
=> "foo"
>> h[2]
=> "foo"
>> h
=> {}

If you need to create a filled hash using {} is enough.  There is no such
thing as a copy constructor.  If you need to explicitely call Hash.new you
need to use #update:

>> h=Hash.new("foo").update(1=>2, 3=>4)
=> {1=>2, 3=>4}
>> h
=> {1=>2, 3=>4}
>> h[111]
=> "foo"

Note that update(1=>2, 3=>4) is a shortcut for update({1=>2, 3=>4})

Kind regards

    robert