From: David Masover <ninja@...>
Date: 2009-12-08T05:54:53+09:00
Subject: Re: convert string into a variable object

On Monday 07 December 2009 02:35:39 pm Ad Ad wrote:
> I have a file with a list of cities in it. The file is a daily feed and
> the cities in it change daily.
[snip]
> this would give us @toronto = 1, @miami = 1, etc.

Is 1 significant? That is, are you trying to count the number of cities, or 
are you just trying to set them to true?

> I have subclasses which would read user input and if that city variable
> has been defined already then move ahead.
> it would be a simple if statement
> if @toronto
> ...
> end

In that case, it would be _much_ more readable if you did

@toronto = true

rather than

@toronto = 1

They'll do the same thing here, but consider this:

@toronto = 0

That would be false, right? Wrong. Anything that's not false or nil is a true 
value in Ruby. You're MUCH better off explicitly using true and false, if 
that's really what you wanted.

If it was meant to be a count, you'd probably want something like:

if @toronto > 0

but I have no idea why a count would make sense here, anyway.

> I could create a hash map too

Yes, you should do that. The downsides of using instance variables for that 
are much larger than the downsides of doing a little extra typing with:

if @cities['toronto']

> but this is the easiest way to do since it

No it's not. You had to come here and ask if it was even possible. You already 
know a hash map is possible, and yo probably already know how to do it.

Just in case someone tells you how to use variables instead, here's one very 
simple reason it's a bad idea: Instance variables have symbols assigned to 
them. Last I checked, symbols aren't garbage collected, so doing it your way 
will result in a (very small) memory leak in your program. That won't happen 
with a hash of strings.

> doesnt require the  creation of any sort of a container variable.

Why is this a problem?

I mean, is it the _creation_ of this that's holding you back? That's a single 
line:

@cities = {}

Put it in initialize.