RFR: 8189088: Add intrusive doubly-linked list utility [v3]

[Daniel D. Daugherty]

On Mon, 9 Oct 2023 06:22:48 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> That rewrite isn't correct.
>> 
>> You _can_ add const values to a non-const list. In fact, you can only add
>> values (const or not) to a non-const list. A const list has type `const
>> IntrusiveList<T, accessor>`, while a non-const list is similar but without the
>> `const` qualifier.
>> 
>> What you can't do is add a const value to a (necessarily non-const) list of
>> non-const elements.  So if T is an unqualified class type, then you can add
>> const values to an `IntrusiveList<const T, accessor>` but not to an
>> `IntrusiveList<T, accessor>`.
>
> Is something like this more clear? In my experience, non-intrusive collections
> with const-qualified elements are uncommon, so I found the implications here
> not immediately obvious.
> 
> 
>  * A const iterator has a const-qualified element type, and provides const
>  * access to the elements of the associated list.  A non-const iterator has an
>  * unqualified element type, and provides mutable element access.  A non-const
>  * iterator is implicitly convertible to a corresponding const iterator.
>  *
>  * A const list provides const iterators and access to const-qualified
>  * elements, and cannot be used to modify the sequence of elements.  Only a
>  * non-const list can be used to modify the sequence of elements.
>  *
>  * A list can have a const-qualified element type, providing const iterators
>  * and access to const-qualified elements.  A const object cannot be added to
>  * a list with an unqualified element type, as that wuold be an implicit
>  * casting away of the const qualifier.

Nit typo: s/wuold/would/

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PR Review Comment: https://git.openjdk.org/jdk/pull/15896#discussion_r1350296773