Persistent list

[Andrei Alexandrescu via Digitalmars-d]

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