From: Mark Probert <probertm@...>
Date: 2003-01-07T02:28:44+09:00
Subject: Re: Compile time constant folding?


Hi, Hal.

At 12:56 AM 1/7/2003 +0900, Hal wrote:

>Redefining things like Fixnum#+ to behave differently may be
>bad coding style... but it is possible. As someone said, when
>software prevents you from doing stupid things, it often
>prevents you from doing very clever things as well.

I think I now understand where my thinking is going off.

We are talking about "constant folding".  When I see the
expressions:

         a = 5
         b = 3
         c = a + b

Then I am seeing the operators (assignment and addition) as
constant as well as values (base 10).  So, I can confidently
say that the above reduces to

         c = 8

However, given that I (the coder) can dynamically change the
operators, there is no way that the compiler can "guess" that
this is true.  So as Dan suggested, I may later redefine "+"
as string cat and mean

         c = "53"

-laugh-

And this seems wrong to me.  If I had meant that, why didn't
I write that in the first place?  Certainly as a maintainer
of code, I would want it to be very clear what is happening.
After all, these values are meant to be constants ...

Ahhh ... here comes Mr Ockham and his razor  ;-)



-mark.