From: dblack@...
Date: 2006-05-04T16:00:23+09:00
Subject: Re: Ruby idiom for attributes / properties

Hi --

On Thu, 4 May 2006, John Lam wrote:

> On 5/4/06, James Britt <james_b@neurogami.com> wrote:
>> 
>> What would you consider to be an attribute?
>
>
> I'm just borrowing the ActiveRecord terminology for attributes. In my mind,
> an attribute == a property. In .NET, a property is a bit of syntactical
> sugar (but also a distinct metadata entity) for a getter and setter method.
>
> Consider this bit of C# code:
>
> class Foo {
> public string StringProperty {
>   get { return "string"; }
>   set { Console.WriteLine("setting a string to " + value); }
> }
> }
>
> This generates under the covers a get_StringProperty and a
> set_StringProperty method.
>
> I would consider it equivalent to this Ruby code:
>
> class Foo
> def string_property
>    'string'
> end
> def string_property=(value)
>   puts "setting a string to #{value}"
> end
> end
>
> The problem is that I can't distinguish a string_property method from any
> other method.

Why is that a problem? :-)  It does demonstrate, though, that the C#
and Ruby samples are not equivalent.

> In .NET, I can walk the property metadata to discover all of
> those properties (and those are things that can be bound to data-aware
> controls in the framework).

In general, the equivalent of a method name with the general format
get_x_property in Ruby is x, and the equivalent of set_x_property in
Ruby is x=.  There's room for debate as to whether there's really such
a thing as an "attribute" at the language level at all in Ruby; I tend
to think not, or very nearly not, since the only support for the
concept, other than the method mechanisms that are in the language
anyway, are the attr_* methods, and to my eyes those are just
convenience methods layered on top of the language.  (Then again, they
are in the language; hence the debate :-)


David

-- 
David A. Black (dblack@wobblini.net)
* Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
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