Very Confused on Template INL File - c++

Question

Okay, I thought I had implementation files for template classes figured out, but apparently not... I have the following files in a VS 2013 C++ solution:
Main.cpp
#include "StateManager.h"
#include "State.h"
enum class Derp {
Herp,
Lerp,
Sherp,
};
int main() {
Game2D::State<Derp>::Context context(5);
Game2D::StateManager<Derp> mgr(context);
return 0;
}
StateManager.h
#pragma once
#include "State.h"
namespace Game2D {
template<typename Id>
class StateManager {
private:
typename State<Id>::Context _context;
public:
explicit StateManager(typename State<Id>::Context context);
};
#include "StateManager.inl"
}
StateManager.inl
template<typename Id>
StateManager<Id>::StateManager(typename State<Id>::Context context) :
_context(context)
{ }
State.h
#pragma once
namespace Game2D {
template<typename Id>
class StateManager;
template<typename Id>
class State {
public:
struct Context {
Context(int);
int data;
};
private:
StateManager<Id>* _manager;
Context _context;
public:
State(StateManager<Id>&, Context);
virtual ~State();
};
#include "State.inl"
}
State.inl
template<typename Id>
State<Id>::Context::Context(int data) {
this->data = data;
}
template<typename Id>
State<Id>::State(StateManager<Id>& manager, Context context) :
_manager(&manager),
_context(context)
{ }
template<typename Id>
State<Id>::~State() { }
Building this Project yields the following errors:
Error 10 error C1903: unable to recover from previous error(s); stopping compilation state.inl 9 1
Error 9 error C2065: 'context' : undeclared identifier state.inl 8 1
Error 7 error C2065: 'manager' : undeclared identifier state.inl 7 1
Error 8 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int state.inl 7 1
Error 6 error C2039: 'State' : is not a member of '`global namespace'' state.inl 6 1
Error 1 error C2143: syntax error : missing ';' before '<' state.inl 2 1
Error 2 error C2988: unrecognizable template declaration/definition state.inl 2 1
Error 3 error C2059: syntax error : '<' state.inl 2 1
Error 4 error C3083: 'Context': the symbol to the left of a '::' must be a type state.inl 2 1
Error 5 error C2039: 'Context' : is not a member of '`global namespace'' state.inl 2 1
Any help on how to fix these errors would be much appreciated!

Answer 1

A wild guess would be that you added your .inl files to you your project as standalone translation units and the compiler attempted to compile them as standalone translation units.
These files make no sense as standalone translation units and they will not compile as such. These are include files (aka header files). They are supposed to be seen as header files by the project. They are not supposed to be compiled directly.