From: dblack@...
Date: 2006-04-26T00:55:32+09:00
Subject: Re: difference between :: and . in calling methods

Hi --

On Wed, 26 Apr 2006, malamute jute wrote:

> newb here.
>
> whats the difference between :: and . in calling methods? like for
> example:
>
>  File::open and File.open
>
> As I understand, you use :: in invoking the constant of a class like
> Math::PI .
>
> Another thing is if i type these in IRB, it returns the same result:
>
>  Object::constants
>  Object.constants
>
> But if i type this, i get undefined method error
>
>  Object.constants.Numeric
>
> whereas this is ok:
>
>  Object::constants::Numeric
>
>
>
> So the question now is when do I use the :: and when do I use the . ?

The :: is never used -- really, I've literally never seen it -- except
when the receiver is a class or module.  In such cases, it's sometimes
used, though I've never understood why, as it makes much more sense to
me just to do:

    receiver.message

regardless of the class of the receiver.

I would love to see :: removed, except for its other purpose of
constant lookup.  (It also occasionally, and understandably, causes
confusion because of that dual role.)


David

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

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