From: "W. Kent Starr" <elderburn@...>
Date: 2001-04-24T12:03:23+09:00
Subject: [ruby-talk:14126] Re: RCR: getClassFromString method

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