std.database

[Rikki Cattermole via Digitalmars-d]

On 02/03/16 4:48 PM, Erik Smith wrote:
> Yes agree that the poly Database is broken - it isn't reference counted
> and I will fix that.

My point was, you shouldn't handle that.

> Your sample code had me wondering if I am missing something else, but I
> can't see another issue yet.  I think the use of classes would
> definitely lead to problems with resources being freed out of order or
> too late.

Currently its use after free. E.g. destructor gets called but there is 
still a copy around.
At the very least it should be an explicit call.

If classes lead to problems, so will structs.

> As far as memory management options, my plan is to work allocators into
> the design and that would seem to provide a lot of options.  I'm having
> a problem at the moment with MallocAllocator's shared interface.  I'm
> not sure why it's shared since malloc/free are thread safe and I can't
> seem to cast away the shared.  I'm sure there is a reason.

Use IAllocator. Don't touch the structs unless you want pain.

Oh and btw final class is your friend.
As an FYI here is my managed memory concept 
https://github.com/rikkimax/alphaPhobos/blob/master/source/std/experimental/memory/managed.d 
its not finished but it mostly works.

Of course I would want to go the more OOP way, sure thats more 
allocations but over all I think there are enough wins that its worth 
it. So if you feel it doesn't fit well with your goal, say so :)

> erik
>
>
> On Wednesday, 2 March 2016 at 03:07:54 UTC, Rikki Cattermole wrote:
>> Okay I've found a problem.
>>
>> Here is some code demonstrating it.
>> http://dpaste.dzfl.pl/022c9e610a18
>>
>> Now take a look again at Database
>> https://github.com/cruisercoder/dstddb/blob/master/src/std/database/poly/database.d#L37
>>
>>
>> Do you see the problem?
>> The solution is simple.
>>
>> The client database type can be a struct or a class. It doesn't matter
>> too much (assuming you're going the way of ranges).
>> But the intermediary representation must be on the heap and should
>> probably use the constructor and not a static create method to get it.
>> This way people can use other memory management solutions and
>> construct it however they like.
>
>