From: dblack@...
Date: 2006-12-29T22:59:02+09:00
Subject: Re: Pickaxe book questions: Symbols and [] method

Hi --

On Fri, 29 Dec 2006, Krekna Mektek wrote:

> Hi list, I've got this probably lame questions.
>
> In the Pickaxe book 2nd ed. they talk about the attr_reader and
> attr_writer on pages 28 and 29 of the book.
>
> There are these attr_reader (eh, methods?) things, which use symbols
> instead of variables, why does Ruby use symbols here, what would be
> the problem if one uses the variable names instead? The symbol is
> pointing to the variable, but the variable is the handle on the data
> (variable value) anyway. Like a symlink pointing to a symlink pointing
> to the actual file.

See Tim's answer.  I just wanted to add a nuance: symbols do not point
to variables.  If you do:

   x = 1
   s = :x

there's no special relation between :x and 1, and no special relation
between s and x.

Internally, Ruby uses :x in a symbol table, indicating that you have a
local variable called x.  However, *that* use of :x has nothing to do
with *your* use of :x.  It's very similar to integers.  If you assign
10 to a variable, and Ruby uses the number 10 somewhere internally,
there's no direct connection.

Symbols are a way of representing text.  That means they can often be
used as method arguments where a method might reasonably be expected
to want some text -- such as a method name.  But the symbol doesn't
"know" that there's a method (or variable) with its name.


David

-- 
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