I'll look into this later this evening or tomorrow. Just wanting to get it noted.

After googling, I believe this is a bug with clang with regard to the mem[i.first] syntax. Didn't track down why though. Rather ambiguous error if you ask me :)

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/map:1276:29: error: call to member function '__construct_node' is ambiguous
__node_holder __h = __construct_node(__k);
^~~~~~~~~~~~~~~~
/Users/alex/code/otl/ethereum/cpp-ethereum/libethereum/State.cpp:106:7: note: in instantiation of member function 'std::__1::map<boost::multiprecision::number<boost::multiprecision::backends::cpp_int_backend<256, 256, 0, 0, void>, 0>,
boost::multiprecision::number<boost::multiprecision::backends::cpp_int_backend<256, 256, 0, 0, void>, 0>, std::__1::less<boost::multiprecision::number<boost::multiprecision::backends::cpp_int_backend<256, 256, 0, 0, void>, 0> >, std::__1::allocator<std::__1::pair<const
boost::multiprecision::number<boost::multiprecision::backends::cpp_int_backend<256, 256, 0, 0, void>, 0>, boost::multiprecision::number<boost::multiprecision::backends::cpp_int_backend<256, 256, 0, 0, void>, 0> > > >::operator[]' requested here
mem[i.first] = RLP(i.second).toInt();
^