[ruby-core:41788] Re: Breaking while loading

Hi

I can't judge whether this is a bug for Ruby runtime or not.
However, I can show reasons why LocalJumpError has occurred.

Reasons why LocalJumpError has occurred are consisting of followings.

1:"break" in proc objects cause LocalJumpError.
2:In your example, $block in A#enum is a proc object
   and $block in A#enum causes "break".

In your example, A#each supposes that &block is a given block to 
Enumerable#take_while. But &block is not a given block to 
Enumerable#take_while.

In your example, &block is "take_while_i" which is internal C function 
of Enumerable#take_while. "take_while_i" is following C function.

/*----------------------------------------------------------*/
static VALUE
take_while_i(VALUE i, VALUE *ary, int argc, VALUE *argv)
{
     if (!RTEST(enum_yield(argc, argv))) rb_iter_break();
     rb_ary_push(*ary, enum_values_pack(argc, argv));
     return Qnil;
}
/*----------------------------------------------------------*/

"take_while_i" consists of following steps.

1: Invokes given block
    (in your example, given block is {|i| i < 3}).
2: Checks a return value of given block.
3: If a return value of given block is "false or nil",
    breaks iteration using "rb_iter_break".
4: If a return value of given block is not "false and nil",
    continues iteration.

$block.call(3) calls "take_while_i", and "take_while_i" calls {|i| i < 
3}. When "i" is 3, {|i| i < 3} returns "false". So, "take_while_i" calls 
"rb_iter_break" to stop iteration. Moreover, "rb_iter_break" throws 
LocalJumpError, because "break" in proc objects cause LocalJumpError.

Nikolai Weibull wrote:
> Hi!
> 
> Here’s a problem that I’m not surprised hasn’t come up before.
> Breaking an iteration from inside a load raises LocalJumpError.
> 
> Is this a bug?
> 
> If not, how do I work around it?
> 
> b.rb:
> $block.call 1
> $block.call 2
> $block.call 3
> 
> class A
>   include Enumerable
> 
>   def each(&block)
>     $block = block
>     load 'b.rb', true
>     self
>   end
> end
> 
> p A.new.take_while{ |i| i < 3 }
> 
> % ruby -v
> ruby 1.9.3p0 (2011-10-30 revision 33569) [x86_64-darwin10.8.0]
> % ruby -w a.rb
> a.rb:22:in `load': unexpected break (LocalJumpError)
>         from a.rb:22:in `each'
>         from a.rb:27:in `take_while'
>         from a.rb:27:in `<main>'
> 
> 
> 
>