From: rashworth <rashworth@...>
Date: 2001-04-24T12:16:34+09:00
Subject: [ruby-talk:14129] Re: RCR: getClassFromString method

What is the Ruby code to produce a 3 row by 2 column matrix
of pixel elements, i.e. black and white?

Thank you.

Bob Ashworth

---------- Original Message ----------------------------------
From: "W. Kent Starr" <elderburn@mindspring.com>
Reply-To: ruby-talk@ruby-lang.org
Date: Tue, 24 Apr 2001 12:03:23 +0900

>On Monday 23 April 2001 18:18, Marko Schulz wrote:
>> On Tue, Apr 24, 2001 at 03:41:23AM +0900, Phil Tomson wrote:
>> > In article <988034673.396094.26164.nullmailer@ev.netlab.zetabits.com>,
>> >
>> > Yukihiro Matsumoto <matz@zetabits.com> wrote:
>> > > [ Should it be encouraged style of programming to retrieve a class
>> > >   by its name in a string? ]
>> >
>> > Well, perhaps it shouldn't be encouraged, I don't know.  I'm not
>> > necessarily an OO purist, I suppose.
>> >
>> > I know that I use this feature in a certain case where I have a class
>> > hierarchy like:
>> >
>> > class Tool
>> >   #methods to handle generic stuff common to PC and UNIX
>> > end
>> >
>> > class Tool_PC < Tool
>> >   #methods do PC specific stuff
>> > end
>> >
>> > class Tool_UNIX < Tool
>> >   #methods do UNIX related stuff
>> > end
>> >
>> > Let's say that early on in the script I figure out what platform I'm
>> > running on, say:
>> > $PLATFORM = "PC"  ($PLATFORM is global so I can instantiate
>> > Tool_"$PLATFORM" objects anywhere later on in the script)
>> >
>> > Then I can instantiate the correct class based on the value of PLATFORM
>> >
>> > There are probably other ways to do this, but getting the Class from a
>> > String seems pretty straitforward in this case - and it is how I've
>> > implemented this.
>> >
>> > So maybe it's not a good 'pure' thing to allow, but it does have its
>> > uses.
>>
>> I would use a factory-method for this:
>>
>>   class ToolFactory
>>
>>      def ToolFactory.getTool
>>        case $PLATFORM
>>          when "Unix" then Tool_Unix
>>          when "PC"   then Tool_PC
>>          else             nil
>>        end
>>      end
>>
>>   end
>>
>>
>> I would favor passing the platform as a parameter since I don't like
>> global variables.
>
>FYI Ruby provides this natively.
>
>ruby -e 'p RUBY_PLATFORM' -> "i586-linux" on my Redhat box.
>
>It will yield similar info on other platforms. The result can be parsed as in
>
>if RUBY_PLATFORM =~ /^(.*)linux$/
>
>etc
>
>Hope tis helps.
>
>Regards,
>
>Kent Starr
>elderburn@mindspring.com
>