ruby​​ koans about_nil.rb - question fr/newbie

Question

我是一个绝对初学者编程。我喜欢红宝石，并设置了koans。本节开始：

def test_you_dont_get_null_pointer_errors_when_calling_methods_on_nil 

请解释这条线：

rescue Exception => ex 

我在本节想通了前两个koans。

Answer 1

该行指出，只要它抛出一个类型为Exception的异常，就可以挽救开始 - 救援块内的代码。事实证明，Exception是所有其他异常继承的*异常（如语法错误，无方法错误等）。正因为如此，所有的例外都将被拯救。然后它将该异常实例存储在变量ex中，您可以在该变量中进一步查看（例如回溯，消息等）。

I'd read this guide on Ruby Exceptions。

一个例子是这样的：

begin 
    hey "hi" 
rescue Exception => ex 
    puts ex.message 
end 
#=> Prints undefined method `hey' for main:Object 

但是，如果开始块中的代码没有给出错误，也不会下井营救分支。

begin 
    puts "hi" 
rescue Exception => ex 
    puts "ERROR!" 
end 
#=> Prints "hi", and does not print ERROR! 

Answer 2

你看了在start of the method?

def test_you_dont_get_null_pointer_errors_when_calling_methods_on_nil 
    # What happens when you call a method that doesn't exist. The 
    # following begin/rescue/end code block captures the exception and 
    # make some assertions about it. 
    begin 
     nil.some_method_nil_doesnt_know_about 
    rescue Exception => ex 
     # What exception has been caught? 
     assert_equal NoMethodError, ex.class 

     # What message was attached to the exception? 
     # (HINT: replace __ with part of the error message.) 
     assert_match(/undefined method/, ex.message) 
    end 
    end