Re: So.... what are we going to do about modules?

From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2022-04-05 13:57:21

On 05/04/2022 14:11, René Ferdinand Rivera Morell via Boost wrote:
> On Tue, Apr 5, 2022 at 7:54 AM Horváth V. <friendlyanon__at_[hidden]>
 wrote:
> 
>> On 2022. 04. 05. 14:46, René Ferdinand Rivera Morell via Boost wrote:
>>> I highly doubt it.
>>
>> Something I noticed is that a lot of people raise compile times as a
>> reason they don't want to use Boost and modules supposedly help with
>> that.
>>
> 
> The gains to be had depend highly on both the code structure and project
> structure (both of the modules and the user code). The gains are almost
> entirely in the re-parsing. I.e. they are not going to help much on the
> template instantiation. Which, IIRC, is the larger of the compile time
> complaints for Boost. But someone would have to do some performance
> analysis  of a good size project that uses Boost in a compiler that
> supports such perf inspection to really know.

To be specific here, what are the gains of Modules over Precompiled 
Headers, which Boost.Build already supports?

Niall's fairly confident answer: little to none, and perhaps even a 
regression as ODR resolution is time expensive.

A better question is whether the compartmentalisation and isolation 
features of Modules are worth adopting Modules?

Niall's fairly confident answer: it *may* be worth it for new codebases, 
but it's very unlikely to be worth retrofitting an existing codebase. An 
awful lot of work for little gain, in my opinion, for most existing 
codebases.

tl;dr; just turn on precompiled headers.

Niall