[Boost-users] [Boost][Container] Why is flat_set default constructor explicit?

Hi all, I just found out that all Boost.Container default constructors are implicit (just as I would expect) except for flat_set. Quoting from [1]: explicit flat_set() noexcept(/*snip*/); Effects: Default constructs an empty container. Why is flat_set different than the other containers? Is this an oversight? FWIW this issue is breaking my C++14 code (for both clang and gcc) when switching from std::set to boost::container::flat_set, minimal repro follows: #include #include <set> #ifndef USE_STD_SET using S = boost::container::flat_set<int>; #else using S = std::set<int>; #endif struct A { int i; S s; }; int main() { A a1; // OK A a2 {0, {{}} }; // OK A b1 {}; // FAILS A b2 {0}; // FAILS A b3 {0, {}}; // FAILS } A f() { return {}; // FAILS } Using Bost 1.64.0 in case that matters. Any help appreciated. [1] http://www.boost.org/doc/libs/1_64_0/doc/html/boost/container/flat_set.html#...