From: Tom Cloyd <tomcloyd@...>
Date: 2008-03-15T16:18:34+09:00
Subject: Re: how to abruptly end a program?

Joel VanderWerf wrote:
> Tom Cloyd wrote:
>> Joel VanderWerf wrote:
>>> Tom Cloyd wrote:
>>>> I read in <Programming Ruby 2nd ed.> (p. 303) - ""If Ruby comes 
>>>> across a line anywhere in the source containing just �_ _END_ _�, 
>>>> with no leading or trailing whitespace, it treats that line as the 
>>>> end of the program�any subsequent lines will not be treated as 
>>>> program code."
>>>>
>>>> That's not what's happening for me. The following -
>>>> _ _END_ _
>>>> __END__
>>>> _END_
>>>>
>>>> all produce the same result for me - "undefined local variable or 
>>>> method"
>>>> That DOES bring the program to an abrupt end, but its rather 
>>>> ungraceful. Is this the intended result - a crash due to an 
>>>> interpreter error?
>>>
>>> What the quote (a bit ambiguous perhaps) means is that the __END__ 
>>> line and following lines are not treated as part of the program 
>>> text. It has nothing to do with control flow. It's like comment 
>>> block that runs to the end of the file without any explicit 
>>> termination. (It's more than that because you can read it with DATA.)
>>>
>> OK, but couldn't ANY uninitialized variable achieve the same messy 
>> result? What's the point? This surely can't be the intended result. 
>> Makes no sense to me.
>
> __END__ by itself on a line shouldn't exit the program. If you're 
> getting that error, maybe there is an extra char on the line. A space 
> perhaps?
>
Yes, that would explain it, but I made sure this problem didn't occur 
from the beginning, which is one reason I'm puzzled. I really don't see 
anything wrong with what I'm feeding the interpreter.

So, I did a different test program -

require 'readline'
puts "test under way\ninput var: "
#opt = readline( "=--> \n")
opt = gets.chomp
puts( opt)
__END__
puts( opt)

result:
test under way
input var:
5
5

Here, we don't get an error. We just get ignored.
This is nuts.

t.

-- 

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