From: Phrogz <phrogz@...>
Date: 2007-11-15T05:10:13+09:00
Subject: Re: "once" meta-method without "module_eval" (Pickaxe)

On Nov 13, 11:23 pm, Greg Weeks <greg.we...@arm.com> wrote:
> Am I right to think that eval-ing strings is retro?

My first dynamically-typed, runtime-interpreted scripting language was
JavaScript. In JavaScript, eval is considered a bad idea. Loading a
string of JavaScript code compiles it to bytecode and then executes
the byte code. Hitting an eval() call in the middle of a program
requires booting up the lexer and bytecode compiler again, to handle
that one string, before it can be run. It's inefficient, and almost
never needed.

I gather the same is not true in Ruby currently. I think (but may be
horribly wrong) that this is not so much because of some excellent
implementation of eval, but a because everything is in the same slow
pool of interpretation.

I'm totally guessing, but I would suspect that at some point in Ruby's
runtime future, startup optimizations/compilations will happen once
only. If this is true (and I know very little about virtual machines
and bytecodes and the actual implementation, so I could be wrong),
then I would suspect that eval of a string (not a block) will incur
undesirable overhead.

For these reasons (my history with eval in JS and my suspicion that it
may become undesirable from a performance standpoint) I personally
never eval strings.