自写的一段ruby元编程的例子

第二段ruby代码的作用是，遍历ruby文件dsl_capybara.rb、dsl_sikuli.rb、dsl_restful.rb及dsl_savon.rb，这些被遍历的文件的共同点是，在模块DSLSet中都分别地定义了一个独有的模块，这些独有的模块中分别定义了一些公有的类方法，如第一段代码所示，注意，各个独有模块所定义的公有的类方法的方法名可能相同，同时，参数也可能相同。
第二段代码会收集嵌套在模块DSLSet中的模块（分布于文件dsl_capybara.rb、dsl_sikuli.rb、dsl_restful.rb及dsl_savon.rb中）所定义的公有类方法，然后，自动在模块DSLSet中直接定义同名的公有的类方法，调用这些类方法时都需要额外地提供一个参数:driver用于选择具体使用嵌套在模块DSLSet中的哪一个模块，然后，自动生成的直接定义在模块DSLSet中的公有的类方法将根据参数:driver的取值不同，去调用相应的子模块的公有的类方法。
总之，第二段代码的作用就是自动生成代码，用于为其他文件中定义的模块的类方法提供一个统一的分发接口。

module DSLSet
    module DSLCapybara
        require 'capybara'
        require 'capybara/dsl'
        require 'capybara/rspec/matchers'

        extend Capybara::DSL   # include keywords defined in Capybara::DSL

        ## override capybara methods or add new methods
        class << self
            def keyword1 # any kind of parameters combination
                #something, maybe 'yield'
                helper
                #something, maybe 'yield'
            end

            def keyword2 # any kind of parameters combination
                #something, maybe 'yield'
            end

            private
                def helper
                    # something
                end
        end
end

require File.join(File.dirname(__FILE__), 'dsl_capybara.rb')
require File.join(File.dirname(__FILE__), 'dsl_sikuli.rb')
require File.join(File.dirname(__FILE__), 'dsl_restful.rb')
require File.join(File.dirname(__FILE__), 'dsl_savon.rb')

module DSLSet
    def default_driver
        @@default_driver
    end

    def set_default_driver driver
        driver = "DSL#{driver.capitalize}" unless driver =~ /^DSL/
        if @@dsl_set.keys.include?(driver.to_sym)
            @@default_driver = driver if (driver != @@default_driver)
        else
            puts "Invalid parameter: #{driver}"
        end
    end

    class << self

        def key_words
           @@dsl_set.values.flatten.uniq
        end

        def drivers
            ds = {}

            @@dsl_set.each do |key, value|
                ds[key] = {}
                dm = DSLSet.module_eval(key.to_s)
                value.each do |v|
                    ds[key][v] = dm.public_method(v).parameters
                end
            end

            ds
        end

        def init
            @@default_driver = "" # "DSLCapybara"
            @@dsl_set = {}
            DSLSet.constants.collect do |cnst_name|
                m = DSLSet.const_get(cnst_name)
                @@dsl_set[cnst_name] = []
                dm = DSLSet.module_eval(cnst_name.to_s)
                dm.singleton_methods.each do |k|
                    @@dsl_set[cnst_name] << k
                end
            end
            key_words.each do |kw|
                define_method(kw) do |*args, &block|
                    driver = @@default_driver
                    ps = []
                    args.each_with_index do |arg, idx|
                        if arg.is_a?(Hash) and arg.keys.include?(:driver)
                            driver = arg[:driver]
                            th = arg.dup
                            th.delete :driver
                            ps << th unless th.empty?
                            ps += args[(idx+1)..-1]
                            break
                        else
                            ps << arg
                        end
                    end

                    driver = "DSL#{driver.capitalize}" unless driver =~ /^DSL/
                    unless driver and @@dsl_set.keys.include?(driver.to_sym)
                        puts "You are setting #{driver} as driver, which is not valid."
                        puts "Please choose a driver from #{@@dsl_set.keys.to_s}"
                        raise "You are setting #{driver} as driver, which is not valid. Please choose a driver from #{@@dsl_set.keys.to_s}"
                    end

                    if @@dsl_set[driver.to_sym] and @@dsl_set[driver.to_sym].include?(kw)
                        mtd = DSLSet.module_eval(driver).public_method(kw)
                        begin
                            mtd.call(*ps, &block)
                        rescue ArgumentError=>e
                            puts "="*50
                            puts e.to_s
                            puts "method \"#{kw}\" of driver \"#{driver}\" was called"
                            puts "expected parameter is #{mtd.parameters.to_s}"
                            puts "actual parameters input are " + ps.to_s
                            project_dir = File.expand_path(File.join(File.expand_path(__FILE__), '..\..'))
                            pd = Regexp.new("^#{project_dir}")
                            e.backtrace.each {|line| puts line if line=~pd}
                            puts "="*50
                        end
                    else
                        raise "#### driver \"#{driver}\" doesn't exist or it has not method \"#{kw}\" ####"
                    end
                end
            end
        end
    end
end

DSLSet.init
include DSLSet

# if __FILE__
# 	puts "\n\n"
# 	puts DSLSet.drivers
# 	puts "\n\n"
# 	puts DSLSet.key_words.sort
# 	puts "\n\n"
# end