It's worse than I thought

[Janice Caron]

On Nov 30, 2007 3:48 PM,  <gide at nwawudu.com> wrote:
> I was under the (wrong) impression that
> 'const(C)' and 'const C'  were synonymous.


Some time ago, Walter started a thread called something like "const
sucks", in which he agreed that D2.007 const was a mess, and promised
to go away and rethink it. He has indeed done that - however, the only
change I can observe is that "head const" has been ditched, along with
the keyword "final". Everything else that was bad about const is still
there.

I find this distressing, because I /love/ what Walter is trying to do.
D-const could be way, way, w-a-y, better than C++ const. I love that
const is transitive. I'm prepared to live without "logical const" and
see what happens. I love the fact that the language distinguishes
between const and invariant, where it makes sense to do that. I love
that "const(int***)***" is so much more concise than C++'s
corresponding "int const*const*const*const***". All of this is GREAT!

But what I hate about it is the confusion between (1) const as a
type-constructor, (2) const as a storage class for variables, (3)
const as a function parameter storage class, and (4) const as a
storage class for member functions. (And ditto for invariant). I
further hate that const/invariant don't apply to declared symbols
(sometimes). Huh!?

So here are my suggestions for clearing up the mess. They are very
simple, clean, and elegant:


(1) ditch "const as a storage class" altogther. Keep "const as a
type-constructor". Stick rigidly to the principle that "const(...)"
means "the stuff in the brackets is const", and nothing else.

(2) allow "const T", where T is a type, to be syntactic sugar for
"const(T)". But it's still just a type constructor.

(3) use the syntax "const(this)" for const member functions. Make
"const(this)" an attribute. Ideally, extend the principle to
"const(anyIdentifier)", but just "const(this)" will do for now.

(4) let "const(C)&" be the syntax for making mutable references to
const classes.

(5) let "const x = y;" be syntactic sugar for "const(typeof(y)) x = y;"

And the same for invariant.


...and that's it!