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Subject: Re: [Boost-users] Multi-Index: custom iterator
From: Sensei (senseiwa_at_[hidden])
Date: 2014-08-26 04:00:58
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;
}
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