https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85517
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Xiaoyi Zhang from comment #0) > 2. Conversion assignment operator=(T&&) > According to [variant.assign] 23.7.3.3 (11.3): if > is_nothrow_constructible<Tj, T> == false && > is_nothrow_move_constructible<Tj> == true, equivalent to > operator=(variant(std::forward<T>(t))). > > Failure case: If Tj has a nothrow move constructor, the standard requires > strong guarantee (that a temporary variant be created first and move it into > *this). The current implementation always invokes emplace(), which has only > basic guarantee. My patch on PR 87431 comment 10 fixes this, by giving emplace the strong guarantee for such types.
