Logan Capaldo
10/11/2006 2:05:00 PM
On Wed, Oct 11, 2006 at 02:40:58PM +0900, Rich Morin wrote:
> "The Ruby Way" (pp. 43-45) shows a couple of different ways
> to generate methods dynamically (using eval). Looking at the
> examples, I began to wonder about different Ways To Do It.
>
> One possibility that occurred to me is to use ERB as a macro
> pre-processor. The book suggests the following code:
>
> if platform == Windows
> def my_action
> action1
> end
> if platform == Linux
> def my_action
> action2
> end
> else
> def my_action
> default_action
> end
> end
>
> Although this is approach is direct and simple, it seems like it
> wouldn't scale very well, given multiple variations. However, I
> think that the following approach might:
>
>
> % cat erb_ml
> #!/usr/bin/env ruby
>
> require 'erb'
>
> def action_D; print "default action\n"; end
> def action_L; print "Linux action\n"; end
> def action_W; print "Windows action\n"; end
>
> action = { :Linux => 'action_L',
> :Windows => 'action_W' }
>
> template = ERB.new <<-EOF
> def my_action
> <%= action[platform] || 'action_D' %>
> end
> EOF
>
> for platform in [ :Linux, :Windows, :Plan9 ] do
> eval template.result(binding)
> print "#{platform.to_s}: "
> my_action
> end
>
> % erb_ml
> Linux: Linux action
> Windows: Windows action
> Plan9: default action
>
>
> Obviously, the "action" hash could be replaced by other
> code-generation and/or -retrieval methods. Is anyone
> here using ERB in this manner? Are there any caveats
> or alternative approaches that I should be aware of?
Bah I say! How does that saying go, "Replace conditionals with
polymorphism"?
class Platform
end
class Linux < Platform
def define_methods
def a
puts "linux"
end
end
end
class Windows < Platform
def define_methods
def a
puts "windows"
end
end
end
class Platform
def self.get_platform
case RUBY_PLATFORM
when /linux/
Linux
when /win32/
Windows
end
end
end
platform = Platform.get_platform.new
platform.define_methods