Conditional execution

gistfile1.txt

$ irb
>> class C
>>   def self.opt?
>>     true
>>   end
>> end
=> nil
>> 
?> module B
>>   def foo
>>     'B'
>>   end
>> end
=> nil
>> 
?> module CB
>>   def self.included(base)
>>     puts 1
>>     self.instance_methods.each do |meth|
?>       puts "=======> meth: #{meth}"
>>       alias_method "__#{meth}", meth
>>       puts 2
>> 
?>       define_method meth do |*args|
?>         puts 3
>>         if C.opt?
>>           puts 4
>>           send("__#{meth}", *args)
>>         else
?>           puts 6
>>           super(*args)
>>         end
>>       end
>>     end
>>   end
>> 
?>   def foo
>>     'CB'
>>   end
>> end
=> nil
>> 
?> class A
>>   include B
>>   include CB
>> end
1
=======> meth: foo
2
=> A
>> 
?> puts "C.opt? => #{C.opt?}"
C.opt? => true
=> nil
>> a = A.new
=> #<A:0x007fad488142d0>
>> 
?> puts a.foo
3
4
CB
=> nil
>> 
?> class C
>>   def self.opt?
>>     false
>>   end
>> end
=> nil
>> 
?> puts "C.opt? => #{C.opt?}"
C.opt? => false
=> nil
>> 
?> puts a.foo
3
6
B
=> nil
>>