From: Morton Goldberg <m_goldberg@...>
Date: 2006-12-12T04:53:26+09:00
Subject: Re: Bug in Ruby or Pickaxe? (was: Re: else inside rescue  is useless?)

On Dec 11, 2006, at 8:55 AM, Robert Klemme wrote:

> def foo(x)
>   begin
>     puts "x=#{x}"
>
>     case x
>       when 0
>         puts "returning"
>         return
>       when 1
>         raise "Some error"
>       when 2
>         raise NameError, "wrong name"
>       when 3
>         break "broken"
>       else
>         puts "do something"
>     end
>
>     puts "unsafe else"
>   rescue NameError
>     puts "name error: #{$!}"
>   else
>     puts "else"
>   ensure
>     puts "leaving!"
>   end
> end
>
> 5.times do |i|
>   begin
>     foo i
>   rescue Exception => e
>     puts "Exception: #{e}"
>   end
> end
>
> With my 1.8.5 I see:
>
> x=0
> returning
> leaving!
> x=1
> leaving!
> Exception: Some error
> x=2
> name error: wrong name
> leaving!
> x=3
> leaving!
> Exception: unexpected break
> x=4
> do something
> unsafe else
> else
> leaving!
>
> What bugs me is that the "else" clause is not executed if it is  
> left via a "return".  Taking the Pickaxe 2nd edition pg. 362  
> literally ("If an else clause is present, its body is executed if  
> no exceptions were raised in code.") it would have to be executed  
> in that case, too.  So, if the interpreter would behave as stated  
> in the book, there was actually a difference between the code at  
> the end of the block and the code inside the else clause.

I would be horrified if the <else> were executed after a <return> --  
<else> is not <ensure>. The Pickaxe book should be probably say: "If  
an else clause is present, its body is executed if no exceptions were  
raised and no exit was made in _code_ ." In fact, I just submitted an  
erratum to this effect on the Pragmatic Programmer site.

> Even in the current situation (where there seems to be no  
> semantically difference) putting code into the else clause instead  
> of the end of the block might have an advantage documentation wise.

Also from Pickaxe: "Exceptions raised during the execution of the  
else clause are not captured by rescue clauses in the same block as  
the else." That seems to be a semantic difference.

Regards, Morton