From: Michael Witrant <mike@...>
Date: 2001-06-21T21:55:09+09:00
Subject: [ruby-talk:16701] Re: cgi.rb cookie access

On Thu, 21 Jun 2001 08:40:45 +0900
"HarryO" <harryo@zipworld.com.au> wrote:

> Say I have two variables called "name" and "value".  Is the correct
way
> to create a variable with the given name and value, to use eval, as in
...
> 
>    eval "#{name} = #{value}"
> 
> or is there a better/cleaner way to do this?
> 

Actually, I think it won't work, because the variable is created in the
eval binding, and is not exported to your local binding. You must assign
it before eval, but since you must use eval to initialize it, you can't.
You can if a method exists to create local variable, but I don't think
so.
But you can create instance variables if you want:

eval "@#{name} = #{value.inspect}"


Another approach I often use in this case is to use a special hash that
allow acces to values through methods. For example:

h = Structash.new # I didn't find a better name for it..
h[:toto]          # => nil
h.toto            # => nil
h.toto = 1.5
h.toto            # => 1.5
h[:toto]          # => 1.5

# In your case:
name = "titi"
value = "tata"
h[name.intern] = value
h.titi            # => "tata"
h[:titi]          # => "tata"

You can access values by using methods, so that your hash looks like a
struct.

Implementing that is quite easy:

class Structash < Hash
  def method_missing(symbol, *args, &block)
    method = symbol.id2name
    if method[-1].chr == "="
      symbol = method[0..-2].intern
      raise "Cannot set #{symbol.id2name}: a method with that name
already exists" if respond_to? symbol
      self[symbol] = args[0]
    else
      if has_key? symbol
        self[symbol]
      else
        #raise NameError, "undefined local variable, method or key
'#{symbol.id2name}' for #{inspect}"
        default
      end
    end
  end
end

In my scripts, I often use that as the default behavior of Hashes.


Mike.
midulo.