On 11/14/2015 03:55 PM, Timon Gehr wrote:
On 11/14/2015 12:10 AM, Andrei Alexandrescu wrote:
...
* Lines 11-12: I came to terms with the notion that some types cannot be
made immutable. We've been trying to do reference counting on immutable
objects for a long time. It's time to acknowledge that true immutability
(which the immutable keyword models) and reference counting don't mix.
Const does work (more below). But overall I'm at peace with the notion
that if you can't live without immutable, I'll refer you to the garbage
collector.
...
I.e. you think it is fine that there can be no list of lists.
T may be const in List!T, so composing with const should work fine.
Anyway, the static assert does not actually do what you intend it to do.
The odd thing is it does as far as I can tell, but the error message is
less than informative. Try it!
* Lines 26-29: The allocator is fundamentally a mutable part of the
container. This is an insufficiency of our type system - we can't say
"this object may be constant, but this reference is to a mutable part of
it". We can't explain that necessity out of existence, and List is part
of the proof. So we need to make that cast legal.
...
Just don't make the method const. (This is not C++.)
I want to allow mutable lists and const lists, just not immutable lists.
It seems to me const has a value even if it doesn't originate from
immutable.
Andrei
