On 2 June 2018 at 07:53, Jim Porter via Boost-users <boost-users@lists.boost.org> wrote:
If it matters, the Appveyor build I'm seeing this with uses Visual Studio 2015 Update 3.

VS2015 has been qualified (quite some time ago already, on reddit) as "buggy" and "to be dropped", because of that, by STL. VS2017 has <optional> and it is ABI-compatible with VS2015.

degski
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