I am attempting to write my own simple reflection system in C++. I have the following test code:
#include <cstdio>
#include <xtr1common>
// common base class
struct TypeDescriptor { };
// specialization for primitive types
template<class T>
struct Primitive : public TypeDescriptor
{
static Primitive<T> Instance;
};
Primitive<int> Primitive<int>::Instance;
struct ReflectedType
{
static TypeDescriptor Reflection;
};
// gets an appropriate TypeDescriptor for a type based on whether it has a Reflection member or not.
// if not, then it expects a Primitive<T> specialization
struct DefaultResolver
{
// used to calculate IsReflected meta-function
template<class T> static char func(decltype(&T::Reflection));
template<class T> static int func(...);
template<class T>
struct IsReflected
{
enum
{
value = (sizeof(func<T>(nullptr)) == sizeof(char))
};
};
// get the TypeDescriptor for a reflected class
template<class T, typename std::enable_if<IsReflected<T>::value, int>::value = 0>
static TypeDescriptor* get()
{
return &T::Reflection;
}
// get the TypeDescriptor for a Primitive<T> if it is not reflected
template<class T, typename std::enable_if<!IsReflected<T>::value, int>::value = 0>
static TypeDescriptor* get()
{
return &Primitive<T>::Instance;
}
};
// helper class that provides type-safe access to a type's TypeDescriptor
template<class T>
struct TypeResolver
{
static TypeDescriptor* get()
{
return DefaultResolver::get<T>();
}
};
int main()
{
// no problems here, obviously
TypeDescriptor* desc = &Primitive<int>::Instance;
// resolves to false, as expected
constexpr bool isIntReflected = DefaultResolver::IsReflected<int>::value;
// resolves to true, as expected
constexpr bool isClassReflected = DefaultResolver::IsReflected<ReflectedType>::value;
// this does not compile
desc = TypeResolver<int>::get();
getchar();
return 0;
}
I am running into issues at the TypeResolver<int>::get()
, with the following errors:
error C2672: 'DefaultResolver::get': no matching overloaded function found
note: while compiling class template member function 'TypeDescriptor *TypeResolver::get(void)'
note: see reference to function template instantiation 'TypeDescriptor *TypeResolver::get(void)' being compiled
note: see reference to class template instantiation 'TypeResolver' being compiled
error C2783: 'TypeDescriptor *DefaultResolver::get(void)': could not deduce template argument for '__formal'
note: see declaration of 'DefaultResolver::get'
I am particularly confused by the second error. I am specifying the template argument, so what am I missing?
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