Forum: Ruby Private attribute or accessor?

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Sam K. (Guest)
on 2005-12-13 19:15
(Received via mailing list)
Hi!

See the following codes.

[1]
class C
  attr_accessor :a
  def f(v)
    @a = v
    ...
  end
end

[2]
class C
  attr_accessor :a
  def f(v)
    a = v
    ...
  end
end


[1] and [2] work exactly same.
I wonder which way is more proper.

In my opinion, if there're accessors (getter and setter), using them in
the class is better than directly accessing the instance data.
However, most codes I've seen access the data directly.

What do you think?

Sam
Joel VanderWerf (Guest)
on 2005-12-13 19:21
(Received via mailing list)
Sam K. wrote:
> class C
>   attr_accessor :a
>   def f(v)
>     a = v
       ^^^^^ this only assigns a local variable

You want:

       self.a = v
Joel VanderWerf (Guest)
on 2005-12-13 19:24
(Received via mailing list)
Sam K. wrote:
> In my opinion, if there're accessors (getter and setter), using them in
> the class is better than directly accessing the instance data.
> However, most codes I've seen access the data directly.
>
> What do you think?

I tend to agree. It's more flexible if you later need to redefine the
accessors to do some extra computation or store the value differently.
Matthew D. (Guest)
on 2005-12-13 19:33
(Received via mailing list)
Sam K. wrote:

>  end
>
>Sam
>
>
Hi Sam,

Just a quick point: your examples don't work the same way.  In [2],
you'll want to replace a = v with self.a = v.

Regards,
Matthew
Sam K. (Guest)
on 2005-12-13 19:54
(Received via mailing list)
Oops!

Right.
a should be self.a.

Sorry!

Sam
Alex F. (Guest)
on 2005-12-13 22:43
(Received via mailing list)
Sam K. wrote:

> In my opinion, if there're accessors (getter and setter), using them in
> the class is better than directly accessing the instance data.
> However, most codes I've seen access the data directly.

Another advantage of using accessor methods (self.foo = ) over variables
(@foo =) is that it can help avoid typo bugs. Variables are initialised
to nil, so if you write @the_variable in one place and later elsewhere
read @thevariable, you don't get an immediate complaint. If you typo an
accessor method, you get an immediate NoMethodError .

I've moved to this style over time - also because it's easier (I find)
to do things using method reflection - eg adding and notifying
observers.

a
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