generic-functions.rb

module X
  module Generic
    Any = BasicObject

    def define_generic_method(name, pattern, &blk)
      generic_methods[name] ||= {}
      generic_methods[name][pattern] = blk
      define_method name do |obj, *args|
        # This will cost O^n, but it may not be too much of a cost given that cases tend to be few
        fn = generic_methods[name].select { |pat, _| pat === obj }.first
        if fn
          obj.instance_exec(*args, &fn[1])
        else
          raise TypeError, "#{name} is not defined for #{obj.inspect}"
        end
      end
    end
    alias generic define_generic_method
    
    def generic_methods
      @generic_methods ||= {}
    end
  end
end

include X::Generic

generic :test, Integer do
  puts "This is a test #{self.inspect}"
end

generic :test, String do
  puts "This is a test #{self.inspect}"
end

generic :test, nil do
  puts "Nil"
end

generic :cool, /^A/ do
  puts "#{self} starts with A"
end

generic :cool, ->(x) { x == 0 } do
  puts "#{self} is zero"
end

generic :cool, (0..10) do
  puts "#{self} is a number between 0 and 10"
end

generic :cool, Any do
  puts "cool on #{self} is not well defined"
end

test 1
test "This is a test"
test nil

cool "Adventure"
cool 5
cool 0
cool 25
cool "Boat"

module Cron
  include X::Generic

  class Job; end
  class HTTPJob < Job; end
  class ScriptJob < Job; end
  
  generic :run, HTTPJob do
    puts "Run #{self} via http"
  end
  
  generic :run, ScriptJob do
    puts "Run #{self} via script interface"
  end
  
  generic :run, Job do
    puts "Run #{self} via shell"
  end

  generic :run, Object do
    puts "Log error #{self} is not a valid Job type"
  end

  module_function :run
end

Cron.run Cron::Job.new
Cron.run Cron::HTTPJob.new
Cron.run Cron::ScriptJob.new
Cron.run 1
Cron.run Object.new