From: Eric Mahurin <eric_mahurin@...>
Date: 2005-09-11T02:32:39+09:00
Subject: Re: quick print type debugging

--- Florian Gro� <florgro@gmail.com> wrote:

> Eric Mahurin wrote:
> 
> > I just took a peek at your code.  This could be quite slow
> > because it uses Binding#of_caller (searches stack, uses
> > continuations) and eval.  I don't particularly like the
> idea of
> > putting code in a string (editors treat it like a string
> rather
> > than code).  Oh, and  having this debug/trace method return
> the
> > expression value would be very useful.
> 
> Why do you think that this is too slow? It's something that
> only happens 
> when debugging. Putting the string into a block doesn't help
> at all 
> because strings are generated at parse-time so you avoid no
> overhead at all.
> 
> True, getting the caller's binding isn't exactly fast, but it
> only 
> happens when debugging. I think you are overrating this as
> you can make 
> trace() a noop when $DEBUG is false. (Just like I do with
> assert { } in 
> ruby-breakpoint.)
> 
> I'm pretty sure that Proc#source is way slower than the 
> Binding.of_caller solution, by the way.


My proposal was that this expression passed to this trace/debug
method always be evaluated (and returned) so that you could
transparently trace any sub-expression in a larger expression. 
I think this would make it an extremely quick way to add traces
anywhere in a piece of code (except LHS of assigns - but you
could trace the whole assign).  I was thinking you might leave
some of this in your code indefinitely and control by a debug
level, but some you may put in temporarily.

I wouldn't mind if getting the file, line, and source of the
expression was slow because that would only be done during
debugging - but not the expression evaluation.

Maybe a way to get around the slowness of Binding#of_caller
would be to modify the string expression after the first call
and give it a "call" method (similar to what I proposed for the
expression in a string in a block).  That way you'd only need
Binding#of_caller and eval once per string expression.


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