Ruby自我和方法定义

我会用Kernel#set_trace_func方法,向你解释幕后发生了什么.首先看下面的代码和输出:

trace = lambda do |event,file,line,id,binding,klass|
    p [event,File.basename(file),line,id,binding,klass]
end


set_trace_func trace

class MyClass
  def self.bar;end
  def one
    def two
    end
  end
end

obj = MyClass.new
obj.one
obj.instance_eval do
  def three
  end
end

输出:

-----------------
----------------
-----------------
-----------------
-----------------
----------------- # part A
["c-call", "test.rb", 9, :singleton_method_added, #<Binding:0x83ab2b0>, BasicObject]
["c-return", "test.rb", 9, :singleton_method_added, #<Binding:0x83aaeb4>, BasicObject]
["line", "test.rb", 10, nil, #<Binding:0x83aab80>, nil]
["c-call", "test.rb", 10, :method_added, #<Binding:0x83aa900>, Module]
["c-return", "test.rb", 10, :method_added, #<Binding:0x83aa07c>, Module]
----------------------------- # part B
["line", "test.rb", 16, nil, #<Binding:0x83a976c>, nil]
["c-call", "test.rb", 16, :new, #<Binding:0x83a9488>, Class]
["c-call", "test.rb", 16, :initialize, #<Binding:0x83a90a0>, BasicObject]
["c-return", "test.rb", 16, :initialize, #<Binding:0x83a8e20>, BasicObject]
["c-return", "test.rb", 16, :new, #<Binding:0x83a8b28>, Class]
---------------------------
---------------------------
--------------------------- # part C
["c-call", "test.rb", 11, :method_added, #<Binding:0x83a7de0>, Module]
["c-return", "test.rb", 11, :method_added, #<Binding:0x83a79f8>, Module]
--------------------------- # part D
["line", "test.rb", 18, nil, #<Binding:0x83a7034>, nil]
["c-call", "test.rb", 18, :instance_eval, #<Binding:0x83a6c10>, BasicObject]
["line", "test.rb", 19, nil, #<Binding:0x83a65f8>, nil]
["c-call", "test.rb", 19, :singleton_method_added, #<Binding:0x83a61d4>, BasicObject]
["c-return", "test.rb", 19, :singleton_method_added, #<Binding:0x83a5ef0>, BasicObject]
["c-return", "test.rb", 18, :instance_eval, #<Binding:0x83a5d4c>, BasicObject]

说明:

看看A部分下面的5行.它只是告诉我们Ruby何时会在类中找到关键字,它会将该方法作为实例方法添加到该类中.这是通过调用hook方法完成的.同样的解释是在C部分下面的两行.defModule#method_added

现在里面发生了obj.instance_eval {..}什么？

好的,如果你看看D部分下面的行,这将被清除.从最后一行,第一行和第二行开始查看.在instance_eval 块中,通过调用hook方法将def third原因third添加为singleton_method对象的一部分.obBasicObject#singleton_method_added

这就是MRI的编写方式.