From: Robert Klemme <shortcutter@...>
Date: 2009-01-13T16:24:15+09:00
Subject: Re: what's the rules re whether a Hash can use either a Symbol or   String to reference the value???

On 12.01.2009 22:02, Stefano Crocco wrote:
> Alle luned́ 12 gennaio 2009, Greg Hauptmann ha scritto:
>> Hi,
>> Getting confused with Hashes a bit.  It seems sometimes I can use both a
>> Symbol or a String to get the value back, but other times the Symbol
>> doesn't work.  Is there any rule re how to remember how Hash handles
>> setting and getting values uses Symbol / String?
>>
>> e.g. hash_variable[:amount] versus hash_variable["amount"]
>>
>> e.g. hash_var = {:amount => 10}, versus hash_var = {"amount" => 10)
> 
> By itself, a hash distinguish between strings and symbols, so if an entry is 
> stored under a string key, you'll only be able to retrieve it using a string 
> key. If the entry has a symbol entry, then it can only be obtained using a 
> symbol key:
> 
> h ={'a' => 1, :b => 2}
> puts h['a'] # => 1
> puts h[:a]  # => nil
> puts h[:b]  # => 2
> puts h['b'] # => nil
> 
> You can setup the hash so that it will work either with strings or symbols. 
> For example:
> 
> hash = Hash.new do |h, k|
>   if k.is_a?(String) and h.has_key? k.to_sym then h[k] = h[k.to_sym]
>   elsif k.is_a?(Symbol) and h.has_key? k.to_s then h[k] = h[k.to_s]
>   else nil
>   end
> end

IMHO there is a downside to assign to the hash in the block because that 
changes the Hash.  This would not work with a frozen Hash for example.

I'd probably rather adjust keys on insertion and retrieval, e.g. always 
change them to Symbols.

Kind regards

	robert

-- 
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