From: "Schüle Daniel" <uval@...>
Date: 2006-10-24T05:45:17+09:00
Subject: Re: File::open and File.open

Robert Klemme schrieb:
> Brad Tilley wrote:
>> What exactly is the difference between these? :: is a class method 
>> while  is an instance method??? If that is so, could someone clarify 
>> this with more detail? I use File.open, but File::open works too.
> 
> The same method (a class method) is called.  It is just a syntactic 
> difference.  So these are the same
> 
> File.open("foo") ...
> File::open("foo") ...
> 
>  > However
>> sometimes, this is not the case which adds to my confusion :) For 
>> example, I can only do Digest::MD5.new() and not Digest.MD5.new() why 
>> is that?
> 
> Because the "." cannot be used for constant lookup:
> 
> irb(main):005:0> File.NONBLOCK
> NoMethodError: undefined method `NONBLOCK' for File:Class
>         from (irb):5
>         from :0
> irb(main):006:0> File::NONBLOCK
> => 16384
> 
> "." is reserved for method invocations.
> 
>> I don't fully understand OO programming... perhaps this is my problem.
> 
> Nah, I think it is rather a minor ambiguity in the language that causes 
> confusion.  Usually people disambiguate it by using "." for methods and 
> "::" for constants only although they could use it for class methods as 
> well.

I was bitten by it more than once
is there more to it ... i mean ambiguity is usually not what one wants 
to have in the language (at least not in the computer language :-)

Regards, Daniel