Re: Getting the index for an element in mutually referencing containers

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-03-15 21:12, Randy Brukardt wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:oaausp$ddn$1@gioia.aioe.org...
>> On 2017-03-14 21:40, Randy Brukardt wrote:
> ...
>> The problem is that the smart pointer type must be anonymous (ad-hoc) like
>> access T is. Otherwise, you get the problem of parallel type hierarchies
>> of the targets and the pointers. And the pointer type must have the
>> interface of the target AKA implicit dereference.
>
> The problem of parallel type hierarchies is one that MUST be solved if one
> is going to program with hierarchies. It IS fundamental to strong typing,
> unlike most of these other issues. We really need a solution to it (I've
> tried some and intend to try more).

I hope you will find something.

> I don't recall ever needing both "strong" or "weak" references to any data
> structure. Most structures only need short-lived references, and the ones
> that need long-lived ones are almost always permanent (only changed between
> runs). Maybe that's because when the only tool you have is an access type,
> every reference looks unchecked and dangerous. :-) But I doubt that many
> problems need or care about the both possibilities.

1. Say you have a tree. A parent holds references to its children. Each 
child holds a reference to its parent. One of these references must be 
weak or you get a circular lock.

2. Another example. Let you attach a monitoring object to the object 
that emits some events/callbacks. Neither may hold another. The monitor 
can take its leave so the object can. In this case both references are weak.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de