Re: [9fans] no const?

["Douglas A. Gwyn" <DAGwyn@null.net>]

Russ Cox wrote:
> Those are the two main needs for volatile, gone, at the
> price of a little optimization, as was pointed out.
> ...
> compiler flag to make everything volatile.  This is basically
> what the Plan 9 compiler does.

Of course, implementors are free to do that.  The reason
they tell me that they don't usually is that many of their
customers demand more aggressive optimization (without the
programmer having to edit source code to get it).  If that
is not important to Plan 9 goals, then its approach is fine
and the "volatile" keyword can then in effect be a no-op.

> In the case of const, ... it certainly feels like
> such things have been added as a sacrifice to the god of
> efficiency rather than for use by mere mortals.

I use "const" frequently, and not because I expect any
additional optimization.  Rather, it documents one
important property of some parameters etc. and enables
diagnostics that routinely detect a certain class of bugs
(which would be undetectable without some programmer-
supplied indication of the intent in the source code).

> And it is a fact that const and volatile are not easily
> understood.  Try explaining to a beginning C programmer
> why "volatile Chan *c" or "Chan volatile *c" both declare
> a pointer to a volatile Chan structure rather than a
> volatile pointer to a Chan structure (which would, obviously,
> be "Chan *volatile c").

That's just a problem in understanding Dennis's contextual
design for C type declarations in general, and is no harder
to explain than anything else of a similar sort in C.