C++ using template type with unordered map

I am new to C++ so this is likely a simple mistake but this code is giving me problems for hours now. I am really just not sure what to try next.

EratosthenesHashMap.h

#pragma once

#include <unordered_map>
#include <boost/functional/hash.hpp>
#include "SieveOfEratosthenes.h"

template<class T>
class EratosthenesHashMap
{

public:
    EratosthenesHashMap(SieveOfEratosthenes& sieve);
    ~EratosthenesHashMap();

    unsigned int addValue(T& value);
    unsigned int getPrime(T& value) const;

private:
    SieveOfEratosthenes *sieve;
    std::unordered_map<T, unsigned int, boost::hash<T>> valueMap;
};

EratosthenesHashMap.cpp

#include "EratosthenesHashMap.h"

EratosthenesHashMap<class T>::EratosthenesHashMap(SieveOfEratosthenes& sieve) 
{
    this->sieve = &sieve;
};

unsigned int EratosthenesHashMap<T>::addValue(T& value)
{
    return 0;
}

unsigned int EratosthenesHashMap<T>::getPrime(T& value) const
{
    return 0;
}

Error:

EratosthenesHashMap.cpp
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\utility(331,10): error C2079: 'std::pair<const T,unsigned int>::first' uses undefined class 'T'
1>        with
1>        [
1>            T=T
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\xhash(305): message : see reference to class template instantiation 'std::pair<const T,unsigned int>' being compiled
1>        with
1>        [
1>            T=T
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\xhash(304): message : while compiling class template member function 'void std::_Hash_vec<std::allocator<std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<_Ty>>>>>::_Tidy(void) noexcept'
1>        with
1>        [
1>            _Ty=std::pair<const T,unsigned int>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\xhash(313): message : see reference to function template instantiation 'void std::_Hash_vec<std::allocator<std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<_Ty>>>>>::_Tidy(void) noexcept' being compiled
1>        with
1>        [
1>            _Ty=std::pair<const T,unsigned int>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\xhash(1933): message : see reference to class template instantiation 'std::_Hash_vec<std::allocator<std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<_Ty>>>>>' being compiled
1>        with
1>        [
1>            _Ty=std::pair<const T,unsigned int>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30037\include\unordered_map(69): message : see reference to class template instantiation 'std::_Hash<std::_Umap_traits<_Kty,_Ty,std::_Uhash_compare<_Kty,_Hasher,_Keyeq>,_Alloc,false>>' being compiled
1>        with
1>        [
1>            _Kty=T,
1>            _Ty=unsigned int,
1>            _Hasher=boost::hash<T>,
1>            _Keyeq=std::equal_to<T>,
1>            _Alloc=std::allocator<std::pair<const T,unsigned int>>
1>        ]
1>C:\Users\jpsie\source\repos\EratosthenesContainer\EratosthenesContainer\EratosthenesHashMap.h(20): message : see reference to class template instantiation 'std::unordered_map<T,unsigned int,boost::hash<T>,std::equal_to<T>,std::allocator<std::pair<const T,unsigned int>>>' being compiled
1>        with
1>        [
1>            T=T
1>        ]

I am trying to create a hashmap as a member variable with key type T, value type unsigned int, and I am using the boost library for a hash function.

>Solution :

It is rather difficult to have a template class split between header file and .cpp file and be easy to consume by callers. Instead, inline your entire template class in EratosthenesHashMap.h:

template<class T>
class EratosthenesHashMap
{

public:
    EratosthenesHashMap(SieveOfEratosthenes& sieve)
    {
        this->sieve = &sieve;
    }
    ~EratosthenesHashMap()
    {
    }

    unsigned int addValue(T& value)
    {
        return 0;
    }

    unsigned int getPrime(T& value) const
    {
        return 0;
    }

private:
    SieveOfEratosthenes* sieve;
    std::unordered_map<T, unsigned int, boost::hash<T>> valueMap;
};