Kinds of containers

[Andrei Alexandrescu via Digitalmars-d]

On 10/21/2015 11:13 AM, Timon Gehr wrote:
> On 10/21/2015 05:08 PM, Timon Gehr wrote:
>> There would be no mutable aliasing.
>
> Here, I mean within the data structure itself. There is nothing wrong with:
>
> class Cell{ int x=0; }
>
> FunSet!Cell a;
> a.insert(new Cell());
> auto b=a;
> foreach(c;a) c.x=1;
> assert(b.x==1);
>
> This is analogous to:
>
> struct SingletonFunSet(T){
>      T element;
> }
>
> auto a=SingletonFunSet!Cell(new Cell());
> auto b=a;
> a.element.x=1;
> assert(b.x==1);
>
> Here, SingletonFunSet!Cell is a value type, but it's constituents might
> not be.

It seems to me that's a departure from traditional persistent data 
structures. Those have immutable elements; far as I can tell you discuss 
containers that only have immutable topology. -- Andrei