[boost] [Modularization][optional][functional] boost::none - what do we want it to be?

Subject: [boost] [Modularization][optional][functional] boost::none - what do we want it to be?
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2014-09-29 12:49:55

Hi Everyone,
I know it may be premature to to think about removing every cycle in Boost,
but while looking at the cycle reports I found that at least one library is
using boost::none, for a purpose different than indicating an uninitialized
boost::optional. It is in Boost.Functional:

https://github.com/boostorg/functional/blob/master/include/boost/functional/factory.hpp

It uses none_t as a default type for a template type parameter Allocator.

My question is: what do we want boost::none_t to indicate, at least in
Boost?
1. A value-semantic alternative to void, that anyone can use?
2. A tag indicating boost::optional<T> without a value?

The answer to this question dictates how we should untie the cycle. I know
it is too soon to care about small cycles right now, but my question is
more about "the principles".

Regards,
&rzej