Compile error when using `pmr::map` with a `std::pair`; works when using a `std::tuple`

[seelabs]

Given the following program:

#include <boost/container/pmr/map.hpp>
#include <boost/container/pmr/monotonic_buffer_resource.hpp>

#include <memory>

int
main()
{
    // tuple works
    // using test_t = boost::container::pmr::map<int, std::tuple<int, int>>;
    // pair does not work
    using test_t = boost::container::pmr::map<int, std::pair<int, int>>;
    boost::container::pmr::monotonic_buffer_resource org_buf;
    test_t org{&org_buf};
    boost::container::pmr::monotonic_buffer_resource copy_buf;
    test_t copy{org, &copy_buf};

    return 0;
}

Results in the following compile error:

/celibs/boost_1_74_0/boost/container/detail/dispatch_uses_allocator.hpp:251:8: error: call to function 'dispatch_uses_allocator' that is neither visible in the template definition nor found by argument-dependent lookup

      (dispatch_uses_allocator)(construct_alloc, arg_alloc, dtl::addressof(p->second), ::boost::forward<V>(y));

However, if test_t is redefined to use a std::tuple instead of a std::pair the program compiles. This is unexpected, as a std::pair and a two element std::tuple should act similarly.

Tested with boost 1.74 and both clang 10 and gcc 10. Also, if I write a similar test program with std::pmr instead of boost::pmr both the pair and tuple versions work.

[igaztanaga]

Thanks for the report!

[mrks]

Just ran into the same issue. Thank you @seelabs for reporting it and @igaztanaga for both fixing it and documenting the tuple workaround!