forked from boostorg/fusion
see: https://github.com/boostorg/fusion/commit/01a2d6557ea65fb4c5ec6f3e50d3340c1c13629d#commitcomment-10697799
see: https://github.com/boostorg/fusion/commit/01a2d6557ea65fb4c5ec6f3e50d3340c1c13629d#commitcomment-10697799