error: no matching function for call to boost ‘hash_value

I am looking to only make use of hash_combine API from boost (for the sake of using a key pair within std::unordered_map) so I copied relevant files to my project (hash.hpp, hash_mix.hpp) and only kept seemingly relevant functions uncommented out (shown later below)

However, I seem to be getting the following error upon using it

error: no matching function for call to ‘hash_value(const Bar&)’

Here's how I have it defined

// file.hpp
#include "hash.hpp"

enum class Bar
{
   // stuff
};

using faultPair = std::pair<Bar, std::string>;
using keyPair = boost::hash<faultPair>;
std::unordered_map<faultPair, int, keyPair> _map;

Usage

// file.cpp

void foo(Bar bar, std::string str, int value)
{
  auto sec = _map.insert({{bar, str}, value}).second; // ERROR: candidate template ignored: could not match 'const std::pair<A, B>' against 'const Bar'
}

Boost lib copied (modified as mentioned above). Copied from here

// hash.hpp
#include "hash_mix.hpp"
// some other headers...
namespace boost
{

template <class T>
inline void hash_combine( std::size_t& seed, T const& v )
{
  seed = boost::hash_detail::hash_mix( seed + 0x9e3779b9 + boost::hash<T>()( v ) );
}

template <class T>
struct hash;

template <class T>
std::size_t hash_value( std::complex<T> const& v )
{
  std::size_t re = boost::hash<T>()( v.real() );
  std::size_t im = boost::hash<T>()( v.imag() );

  return re + hash_detail::hash_mix( im );
}


// pair
template <class A, class B>
std::size_t hash_value( std::pair<A, B> const& v )
{
  std::size_t seed = 0;

  boost::hash_combine( seed, v.first );
  boost::hash_combine( seed, v.second );

  return seed;
}

// boost::hash
template <class T> struct hash
{
  typedef T argument_type;
  typedef std::size_t result_type;

  std::size_t operator()( T const& val ) const
  {
    return hash_value( val );
  }
};
}

Errors:

1.

seed = boost::hash_detail::hash_mix( seed + 0x9e3779b9 + boost::hash<T>()( v ) );

In instantiation of ‘std::size_t boost::hash::operator()(const T&) const [with T = Bar; std::size_t = long unsigned int]’:

required from ‘void boost::hash_combine(std::size_t&, const T&) [with T = Bar; std::size_t = long unsigned int]’

boost::hash_combine( seed, v.first );

required from ‘std::size_t boost::hash_value(const std::pair<_T1, _T2>&) [with A = Bar; B = std::__cxx11::basic_string; std::size_t = long unsigned int]’

return hash_value( val );

required from ‘std::size_t boost::hash::operator()(const T&) co开发者_开发百科nst [with T = std::pair<Bar, std::__cxx11::basic_string >; std::size_t = long unsigned int]’

return hash_value( val );

error: no matching function for call to ‘hash_value(const std::__cxx11::basic_string&)’

---

Some compiler notes:

1.

return hash_value( val );

mismatched types ‘const std::complex<_Tp>’ and ‘const Bar’

std::size_t hash_value( std::complex<T> const& v )

template argument deduction/substitution failed:

return hash_value( val );

mismatched types ‘const std::pair<_T1, _T2>’ and ‘const Bar’