+1 to Ben Craig's request for a motivational example. A couple of other points to consider:

* Could it be a static member function rather than a const member function? If I understand, this seems like it might be data that you'd want to use to create a container, rather than a question you'd want to ask of an existing container.

* Either way, I imagine that it could and should be a constexpr function.

Regards,
Ben Saks



Sent from my Galaxy


-------- Original message --------
From: Ben Craig via SG14 <sg14@lists.isocpp.org>
Date: 11/25/21 11:46 AM (GMT-05:00)
To: sg14@lists.isocpp.org
Cc: Ben Craig <ben.craig@ni.com>
Subject: Re: [SG14] sizeof_block_metadata function, colony/hive, advice wanted

If you can provide a short, motivational chunk of code that shows how it would be used, then that would make it a lot easier to answer the question about whether it's useful or not.  I suspect the function may be providing something that is easy for the implementation to provide, but very hard for a user to use.

I suspect that this is trying to help the user solve an optimization problem, where they are trying to minimize the amount of total memory used for a given range of element counts.  If that's the case, then write a short code snippet that either solves, or hints at the solution to that problem.

> -----Original Message-----
> From: SG14 <sg14-bounces@lists.isocpp.org> On Behalf Of Matt Bentley via
> SG14
> Sent: Wednesday, November 24, 2021 7:35 PM
> To: Low Latency:Game Dev/Financial/Trading/Simulation/Embedded Devices
> <sg14@lists.isocpp.org>
> Cc: Matt Bentley <mattreecebentley@gmail.com>
> Subject: [EXTERNAL] [SG14] sizeof_block_metadata function, colony/hive,
> advice wanted
>
> Hi all,
> thinking about including a
> size_type sizeof_block_metadata(const size_t block_size)
>
> function for colony/hive, as this would allow the user to ascertain the
> amount of memory used by a memory block's metadata in colony (including
> skipfield), given the number of elements stored in that memory block.
> This is less important for colony which is a fixed implementation, more
> important for std::hive which could potentially have many alternative
> implementations and these might not be visible to the user in text form.
>
> The idea was that if someone knows how much memory is used by each
> block outside of the actual memory used to store the elements, that might
> aid in terms of knowing how much cache space is used by the metadata and
> people might be able to make better decisions about the min/max capacities
> of memory blocks (if they are specifying these manually) on that basis.
>
> The function would throw an exception if the block_size specified was
> outside the minimum/maximum block capacity ranges.
>
> My main question to you is whether this function is worth including - as it
> adds yet another function to the codebase.
> Thanks,
> M@
>
>
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