Dropping support for InPlaceFactory from Optional

From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2023-10-01 10:46:08

Hi Everyone,
I would like to get the community's advice on removing the support for
InPlaceFactory from Boost.Optional.

The motivation for this is to reduce dependencies among Boost libraries.
Boost.Optional is surprisingly heavy. This is mostly due to the dependency
on InPlaceFactory and OptionalPointee from Boost.Utility.

https://pdimov.github.io/boostdep-report/develop/module-weights.html#weight:12

InPlaceFactory (
https://www.boost.org/doc/libs/1_83_0/libs/utility/doc/html/utility/utilities/in_place_factory.html)
used to be a workaround for the missing "perfect forwarding" in C++03, it
emulated both "universal references" and variadic templates. It is
unnecessary for C++11 where Boost.optional offers a superior interface. But
removing the support for InPlaceFactory would break code for people that
happen to use it. When the user switches to C++11 (C++03 support is
deprecated for Boost.Optional) they should expect their programs to still
compile. But if I remove the InPlaceFactory, it forces the users to change
their code, even if they are already on C++11.

Can InPlaceFactory be moved to a separate library? Or is it so useless now
that it has to be eradicated even at the cost of breaking users' code?

I would welcome any suggestions.

Regards,
&rzej;