c++ - Workaround GCC 5.5 tuple initialisation bug

Consider this code:

  std::vector<
          std::tuple,
                     std::vector,

                     std::vector>
        > foo = {
        {{2, 1, 2, 3},   {1, 2},  {2, 3}},
        {{2, 3, 4, 0},   {3},     {2, 3, 4}},
        {{2, 3, 4, 0},   {0},     {3, 4, 0}},
      };

In Clang, and GCC 6 or later it compiles fine. In GCC 5.5 it gives this error:

 In function 'int main()':

:16:4: error: converting to
          'std::tuple >,
                      std::vector >,
                      std::vector > >'
      from initializer list would use explicit constructor
          'constexpr std::tuple<  >::tuple(const _Elements& ...)
     [with _Elements = {
           std::vector >, std::vector >, std::vector >}]'


    };

    ^

Why is this and how can I work around it?

Answer

One possible workaround is to call tuple constructor explicitly:

using bar = std::tuple,
                       std::vector,
                       std::vector>;
std::vector foo = {
    bar{{2, 1, 2, 3},   {1, 2},  {2, 3}},
    bar{{2, 3, 4, 0},   {3},     {2, 3, 4}},
    bar{{2, 3, 4, 0},   {0},     {3, 4, 0}},
};

(Live demo)