D const design rationale

[Bill Baxter]

Sean Kelly wrote:
> Walter Bright wrote:
>> Sean Kelly wrote:
>>> Walter Bright wrote:
>>>> In C++, sometimes const means invariant, and sometimes it means 
>>>> readonly view. I've found even C++ experts who don't know how it works.
>>> Odd.  The C++ system always seemed extremely simple to me.
>>
>> It isn't. I run into people all the time who are amazed to discover 
>> that const references can change. 

I was surprised to find that p->q[0]=5 is always ok for a
const C*p.  Learned that from reading the const doc just now.


> Matter of opinion, I suppose.  The C++ design was immediately clear to 
> me, though it obviously wasn't for others.  I grant that the aliasing 
> problem can be confusing, but I feel that it is a peripheral issue.

I vaguely remember C++'s const taking some time for me to internalize. 
But it seems natural now.  So I'm not too worried about it.  I also have 
a feeling that invariant won't show up very often except at the 
module-level scope.  So I'm not so worried about how to grok the odd 
combinations of const/invariant and what they mean.  I have trouble with 
groking "int * const * const **foo" in C++ but that's never caused me 
any problem in an actual programming task.  In the end there are just a 
handful of common usages.  It might be nice to have these collected and 
documented somewhere.

--bb