From: badboy <badboy@...>
Date: 2009-01-13T06:03:20+09:00
Subject: Re: what's the rules re whether a Hash can use either a Symbol or String to reference the value???

Greg Hauptmann schrieb:
> 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)
> 
> 
first:
every time you call hash_var["amount"] a new string is created.
But if you call with :amount, :amount will always be the same object.

next:
the default Hash class does not mix String- and Symbol-Keys.
so
   hash_var[:amount] = 10
   hash_var["amount"] = 11
   hash_var[:amount] != hash_var["amount"] # => true

but for example ActiveSupport (used in Rails) defines a class 
HashWithIndifferentAccess.
there all Symbol-keys gets converted to a String, so that either :amount 
or "amount" point to the same entry.

So if you want to know how to handle it, ask the variable for its class 
(if someone uses monkey-patching you will lose =P)