On Fri, 13 Apr 2018 at 08:24 Edward Diener via Boost-users <boost-users@lists.boost.org> wrote:

The reason some libraries use boost::shared_ptr rather than
std::shared_ptr has nothing to do with supporting VC7.1 at all. The most
obvious reason is that a given library works with code at the c++03
level and does not require c++11 on up. You may feel that this is wrong,
but this is another issue entirely than still having to support VC7.1.

There are of course other reasons for choosing the boost variant over the std variant, even outside of boost. Four that often influence me are:

- Boost often offers an extended API

- Boost components can be forward declared

- Boost offers the same implementation across platforms

- I can fix a boost version should I need to

My projects tend to reach for boost over std for most components as a result of this.

-- chris