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。

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1. module DSLSet
2.     module DSLCapybara
3.         require 'capybara'
4.         require 'capybara/dsl'
5.         require 'capybara/rspec/matchers'
6. 
   
7.         extend Capybara::DSL   # include keywords defined in Capybara::DSL
   
8. 
   
9.         ## override capybara methods or add new methods
10.         class << self
11.             def keyword1 # any kind of parameters combination
12.                 #something, maybe 'yield'
13.                 helper
14.                 #something, maybe 'yield'
15.             end
16. 
    
17.             def keyword2 # any kind of parameters combination
18.                 #something, maybe 'yield'
19.             end
20. 
    
21.             private
22.                 def helper
23.                     # something
24.                 end
25.         end
26. end

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1. require File.join(File.dirname(__FILE__), 'dsl_capybara.rb')
2. require File.join(File.dirname(__FILE__), 'dsl_sikuli.rb')
3. require File.join(File.dirname(__FILE__), 'dsl_restful.rb')
4. require File.join(File.dirname(__FILE__), 'dsl_savon.rb')
5. 
   
6. module DSLSet
7.     def default_driver
8.         @@default_driver
9.     end
10. 
    
11.     def set_default_driver driver
12.         driver = "DSL#{driver.capitalize}" unless driver =~ /^DSL/
13.         if @@dsl_set.keys.include?(driver.to_sym)
14.             @@default_driver = driver if (driver != @@default_driver)
15.         else
16.             puts "Invalid parameter: #{driver}"
17.         end
18.     end
19. 
    
20.     class << self
21. 
    
22.         def key_words
23.            @@dsl_set.values.flatten.uniq
24.         end
25. 
    
26.         def drivers
27.             ds = {}
28. 
    
29.             @@dsl_set.each do |key, value|
30.                 ds[key] = {}
31.                 dm = DSLSet.module_eval(key.to_s)
32.                 value.each do |v|
33.                     ds[key][v] = dm.public_method(v).parameters
34.                 end
35.             end
36. 
    
37.             ds
38.         end
39. 
    
40.         def init
41.             @@default_driver = "" # "DSLCapybara"
42.             @@dsl_set = {}
43.             DSLSet.constants.collect do |cnst_name|
44.                 m = DSLSet.const_get(cnst_name)
45.                 @@dsl_set[cnst_name] = []
46.                 dm = DSLSet.module_eval(cnst_name.to_s)
47.                 dm.singleton_methods.each do |k|
48.                     @@dsl_set[cnst_name] << k
49.                 end
50.             end
51.             key_words.each do |kw|
52.                 define_method(kw) do |*args, &block|
53.                     driver = @@default_driver
54.                     ps = []
55.                     args.each_with_index do |arg, idx|
56.                         if arg.is_a?(Hash) and arg.keys.include?(:driver)
57.                             driver = arg[:driver]
58.                             th = arg.dup
59.                             th.delete :driver
60.                             ps << th unless th.empty?
61.                             ps += args[(idx+1)..-1]
62.                             break
63.                         else
64.                             ps << arg
65.                         end
66.                     end
67. 
    
68.                     driver = "DSL#{driver.capitalize}" unless driver =~ /^DSL/
69.                     unless driver and @@dsl_set.keys.include?(driver.to_sym)
70.                         puts "You are setting #{driver} as driver, which is not valid."
71.                         puts "Please choose a driver from #{@@dsl_set.keys.to_s}"
72.                         raise "You are setting #{driver} as driver, which is not valid. Please choose a driver from #{@@dsl_set.keys.to_s}"
73.                     end
74. 
    
75.                     if @@dsl_set[driver.to_sym] and @@dsl_set[driver.to_sym].include?(kw)
76.                         mtd = DSLSet.module_eval(driver).public_method(kw)
77.                         begin
78.                             mtd.call(*ps, &block)
79.                         rescue ArgumentError=>e
80.                             puts "="*50
81.                             puts e.to_s
82.                             puts "method \"#{kw}\" of driver \"#{driver}\" was called"
83.                             puts "expected parameter is #{mtd.parameters.to_s}"
84.                             puts "actual parameters input are " + ps.to_s
85.                             project_dir = File.expand_path(File.join(File.expand_path(__FILE__), '..\..'))
86.                             pd = Regexp.new("^#{project_dir}")
87.                             e.backtrace.each {|line| puts line if line=~pd}
88.                             puts "="*50
89.                         end
90.                     else
91.                         raise "#### driver \"#{driver}\" doesn't exist or it has not method \"#{kw}\" ####"
92.                     end
93.                 end
94.             end
95.         end
96.     end
97. end
98. 
    
99. DSLSet.init
100. include DSLSet
101. 
     
102. # if __FILE__
103. # puts "\n\n"
104. # puts DSLSet.drivers
105. # puts "\n\n"
106. # puts DSLSet.key_words.sort
107. # puts "\n\n"
108. # end