From: Sam Roberts <sroberts@...>
Date: 2003-06-05T09:47:01+09:00
Subject: Re: case of sub! not working

Somebody suggested that strings returned by ENV#[] be frozen,
emphasizing that they can't be changed. I like that idea, it
seems to get rid of any need to add an explanation of all
this to the FAQ.

Sam

> I'll take a stab at it. I can't promise that
> what I say is correct.
> 
> The illusion of ENV being a simple hash is a 
> good one. But remember that when you get/set
> environment variables, ultimately you are 
> calling getenv/setenv or some equivalent.
> 
> It's one thing to do an ENV[x] = y, as []=
> is a method invoked on ENV. We can trap the
> change and call setenv.
> 
> But if ENV[x] refers to a string, and I change
> that string... then ENV itself hasn't changed.
> In fact, for an in-place change, even the 
> object id of the string hasn't changed.
> 
> To accomplish something like ENV[x].sub! working
> intuitively, we would have to monitor every 
> string object referenced by ENV and watch to see
> when any of them was changed.
> 
> Perhaps possible but impractical and inefficient.
> 
> Hal
> 
>