ruby - begin、rescue 和 => 符号是如何工作的？

Question

在 Ruby koans 的第 6 个练习中，有:

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 __, ex.class

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

我不知道那里的 => 符号是什么？ begin 和 rescue 我不清楚。

Answer 1

当出现问题时，您可以“引发异常”

def do_it
  # ..
  raise Exception.new("something went wrong !") if something_went_wrong
end

如果 something_went_wrong 为真，这将停止程序的执行。如果您不处理异常。

要处理您使用“rescue Exception”的异常

begin
  do_it
rescue Exception
  puts "Something went wrong, but go on anyway"
end

如果你需要处理异常，你可以用“=>”给它一个名字

begin
  do_it
rescue Exception => ex
  # Now "ex" is the name of the Exception. And "ex.inspect" inspects it.
  puts "Something went wrong, #{ex.inspect}, .."
end

如果你喜欢ruby koans，你可能也会喜欢rubymonk在线教程。在“Ruby Primer: Ascent”中有一节关于异常的类(class)。