From: Robert Klemme <bob.news@...>
Date: 2005-03-16T16:24:48+09:00
Subject: Re: eval/binding question


"Stefan Kaes" <skaes@gmx.net> schrieb im Newsbeitrag
news:4237CBC1.9070209@gmx.net...
> Yukihiro Matsumoto wrote:
>
> >Hi,
> >
> >In message "Re: eval/binding question"
> >    on Wed, 16 Mar 2005 02:45:41 +0900, Stefan Kaes <skaes@gmx.net>
writes:
> >
> >|In the real environment, the names of the locally assigned variables
can
> >|not be determined in advance, of course.
> >
> >I'm sorry to say you can't pre-compile eRB allowing local variable set
> >not determined in advance.  I know allowing this will make your
> >program 25% faster, but this also would make any other programs
> >slower.
> >
> >
> I fail to see why it would make other code slower. I am convinced with a
> proper compiler implementation there would'nt be any speed difference
> for local variables introduced via explicit assignment. Access to
> predeclared variables would use an optimized  access method, whereas
> access to variable names whose declaration point cannot be determined by
> statical program analysis would use a less efficient access method.

I wonder in which cases this would be useful.  This code is artificial,
since one would never write test2 like you did:

    def test2
      eval "x=25"
      print "x=#{x}\n"
    end

If you write something similar but with a string coming from somewhere
else

    def test2(s)
      eval s
      print "x=#{x}\n"
    end

you know already that "s" must contain an assignment to "x".  So it's not
a problem to predeclare it IMHO.

I don't really see which real world problems would be solved with a more
complex lookup for locals, which would make the second variant succeed
without the explicit declaration of "x".

Kind regards

    robert