On 8/25/14, 9:14pm, Joaquin M Lopez Munoz wrote:
One easy way to get something roughly equivalent in many situations to what you want is (warning, uncompiled):
template<typename Tag> typename boost::multi_index::index<DataStorage,Tag>::index::const_iterator myfind(const DataStorage& s,unsigned int v) { return s.template get<Tag>().find(v); }
...
auto it=myfind<byMSB>(storage,MSB(value128bits));
myfind returns a different iterator type depending on the tag you specify when calling it.
Hi Joaquin, and thanks as usual! I am trying your solution with a member function, but I get the following error: /Users/sensei/Documents/Projects/scratch/indexed/indexed/main.cpp:145:16: error: no matching member function for call to 'myfind' auto q = d.myfind<byMSB>(Data::storage(1, 30, 30)); ~~^~~~~~~~~~~~~ /Users/sensei/Documents/Projects/scratch/indexed/indexed/main.cpp:125:5: note: candidate template ignored: substitution failure [with Index = byMSB]: no type named 'const_iterator' in 'boost::multi_index::index<boost::multi_index::multi_index_container<unsigned __int128, boost::multi_index::indexed_by<boost::multi_index::hashed_non_unique<boost::multi_index::tag<byMSB, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::multi_index::global_fun<unsigned __int128, unsigned long long, &Data::msb>, mpl_::na, mpl_::na>, boost::multi_index::hashed_non_unique<boost::multi_index::tag<byHSB, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::multi_index::global_fun<unsigned __int128, unsigned short, &Data::hsb>, mpl_::na, mpl_::na>, boost::multi_index::hashed_non_unique<boost::multi_index::tag<byLSB, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::multi_index::global_fun<unsigned __int128, unsigned long long, &Data::lsb>, mpl_::na, mpl_::na>, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, std::__1::allocator<unsigned __int128> >, byMSB>' myfind(unsigned int v) //const DataStorage& s, unsigned int v) ^ 1 error generated. I changed your definition to this, I think the modifications are really trivial, but I doubt my code makes sense now: template<typename Index> typename boost::multi_index::index<DataStorage, Index>::index::const_iterator myfind(unsigned int v) { return storage_.template get<Index>().find(v); } The entire code is below. As I gave up on writing an iterator (see below), I am trying to do the best I can do with some cosmetic code. The part in #if 0 / #endif is my failed attempt to use equal_range with something more palatable, but it fails again.
Note that this is *not* the same as returning a custom iterator type that is able to traverse the different indices DataStorage is comprised of: in order to do that you need to implement an iterator class with *type erasure*, which has a run-time penalty and is not entirely trivial to write. If you want to know more about type-erasing iterators, take a look at, for instance, adobe::any_iterator:
I guess I won't be writing a type-erasure-based custom iterator: I don't like run-time overhead if I can avoid this :) Thanks! === SOURCE CODE === #include <boost/multi_index_container.hpp> #include <boost/multi_index/global_fun.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/hashed_index.hpp> #include <functional> #include <iomanip> #include <iosfwd> #include <tuple> #include <list> #include <utility> #include <iterator> #include <type_traits> typedef __uint128_t Storage; struct byMSB { }; struct byHSB { }; struct byLSB { }; const int MSBbits = 60; const int HSBbits = 8; const int LSBbits = 60; template <unsigned int N> struct Mask { static Storage const value = (static_cast<Storage>(1) << N) - 1; }; template <> struct Mask<0> { static Storage const value = 0; }; // Dump to stream std::ostream &operator<<(std::ostream &os, const Storage &s) { uint64_t msb = (s >> 64), lsb = (s & 0xFFFFFFFFFFFFFFFF); os << "0x"; os << std::hex << std::setfill('0') << std::setw(16) << msb; os << " "; os << std::hex << std::setfill('0') << std::setw(16) << lsb; return os; } class Data { public: Data() {}; // Get the msb static uint64_t msb(Storage v) { return static_cast<uint64_t>((v >> (HSBbits + LSBbits))); } // Get the hsb static uint16_t hsb(Storage v) { return static_cast<uint16_t>((v >> (LSBbits)) & Mask<HSBbits>::value); } // Get the lsb static uint64_t lsb(Storage v) { return static_cast<uint64_t>(v & Mask<LSBbits>::value); } // Returns a storage type static Storage storage(uint64_t msbv, uint16_t hsbv, uint64_t lsbv) { return static_cast<Storage>((static_cast<Storage>(msbv) & Mask<MSBbits>::value) << (HSBbits + LSBbits) | (static_cast<Storage>(hsbv) & Mask<HSBbits>::value) << (LSBbits) | (static_cast<Storage>(lsbv) & Mask<LSBbits>::value)); } // Insert a new item void insert(uint64_t msbv, uint16_t hsbv, uint64_t lsbv) { storage_.insert(storage(msbv, hsbv, lsbv)); } private: // Storage type with indexing typedef boost::multi_index::multi_index_container< Storage, boost::multi_index::indexed_by< // Hashed by msb/hsb/lsb boost::multi_index::hashed_non_unique<boost::multi_index::tag<byMSB>, boost::multi_index::global_fun<Storage, uint64_t, &Data::msb>>, // 0 boost::multi_index::hashed_non_unique<boost::multi_index::tag<byHSB>, boost::multi_index::global_fun<Storage, uint16_t, &Data::hsb>>, // 1 boost::multi_index::hashed_non_unique<boost::multi_index::tag<byLSB>, boost::multi_index::global_fun<Storage, uint64_t, &Data::lsb>> // 2 > > DataStorage; DataStorage storage_; public: #if 0 template <class Index> using const_iterator = typename DataStorage::hashed_index; template <class Index> using iterator = std::pair<const_iterator<Index>, const_iterator<Index>>; template <class Index> iterator<Index> use(Storage v) { auto &p = storage_.template get<Index>(); auto q = p.equal_range(msb(v)); return iterator<Index>(q); }; #endif template<typename Index> typename boost::multi_index::index<DataStorage, Index>::index::const_iterator myfind(unsigned int v) { return storage_.template get<Index>().find(v); } }; int main(int argc, const char * argv[]) { Data d; d.insert(1, 0, 0); d.insert(2, 1, 0); d.insert(3, 0, 0); d.insert(1, 1, 1); d.insert(4, 0, 4); d.insert(5, 4, 3); d.insert(1, 9, 9); auto q = d.myfind<byMSB>(Data::storage(1, 30, 30)); return 0; }