C++11 linker error VS17 - visual-studio

Question

#include <iostream>
#include <fstream>
#include <type_traits>
#include <Windows.h>
#include "abase.h"
using namespace std;
class Storage {
string _path;
public:
Storage(string path);
~Storage() = default;
template <typename T >
bool writeFile(string fileName,
typename enable_if<is_base_of<ABase, T>::value, T >::type* data);
}
Definition...
#include "storage.h"
Storage::Storage(string path)
{
this->_path = path;
}
template <typename T >
bool Storage::writeFile(string fileName,
typename enable_if<is_base_of<ABase, T>::value, T >::type* data){
return true;
}
Im still getting error by Linker:
LNK2019 unresolved external symbol "public: bool __thiscall
Storage::writeFile(class std::basic_string,class std::allocator >,class AFile*)"
(??$writeFile#VAFile###Storage##QAE_NV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##PAVAFile###Z)
referenced in function _main
Why am i getting it if code is looking right. Its generic definition of method in a class and Im trying to constrain class type passing to the method.
And the AFile is inherited from ABase.
ABase is abstract class.
Simple usage in main:
Storage* s = new Storage("C:\\aPath...");
AFile* afile = new AFile();
s->writeFile<AFile>("a.txt", afile);

Answer 1

To solve your linking error you can explicitly instantiate[1] your template member function in the Storage.cpp like this:
template
bool Storage::writeFile<AFile>(string fileName,
enable_if<is_base_of<ABase, AFile>::value, AFile>::type* data);
so the compiler creates the function and the linker can find.
It's better to move the definitions in the header file - Why can templates only be implemented in the header file?.