From: Yuri Leikind <YuriLeikind@...>
Date: 2003-01-24T03:51:44+09:00
Subject: Re: emulating C preprocessor's #if

On Fri, 24 Jan 2003 03:36:04 +0900
Joel VanderWerf <vjoel@PATH.Berkeley.EDU> wrote:

> Usually, when writing ruby code, I don't worry about conditional 
> compilation, and just use a run-time test. But for some critical code,
> I prefer to factor the conditional out to compile time. Unfortunately,
> 
> this can require either a lot of duplication of source code, or 
> awkwardly factoring out sub-methods which are conditionally compiled. 
> Sometimes, the following approach is more convenient:
> 
> module M
>    solaris = (RUBY_PLATFORM =~ /solaris/i)
>    linux = (RUBY_PLATFORM =~ /linux/i)
>    windows = (RUBY_PLATFORM =~ /win/i)
> 
>    module_eval %{
>      def self.print_platform
>        print "Platform is... "
>        #{
>          if solaris then %{
>            puts "solaris"
>          }
>          elsif linux then %{
>            puts "linux"
>          }
>          elsif windows then %{
>            puts "windows"
>          }
>          else %{
>            puts "unknown"
>          }
>          end
>        }
>      end
>    }
> end
> 
> M.print_platform


Perhaps I might have misunderstood the main point of your letter, but I
think Ruby is dynamic enough to do what you want without any other
changes in the core language:

module M

   def M.print_platform
      print "Platform is..." + M.platform_dependent_code() + "\n"
   end

   case RUBY_PLATFORM
   
      when /solaris/i then
         def M.platform_dependent_code
            "Solaris"
         end
      when /linux/i then
         def M.platform_dependent_code
            "Solaris"
         end
      when /win/i then
         def M.platform_dependent_code
            "Solaris"
         end
      else
         def M.platform_dependent_code
            "unknown"
         end
     end
end

M.print_platform



___
Best regards,
Yuri Leikind

The debate rages on: Is PL/I Bachtrian or Dromedary?