Styjun

I'm still learning about templates. I'm not sure whether you can declare/(automatically define) a function inside a class (method) using a template. That is, I have a function template defined like this, for example:

template<typename T>
T getT() 
 T result;
 return result;

And a class, where I want the "new function" to be created, based on the template, like this:

class World
public:
 World();
 ~World();
 getT<int>; //"Magically" create new function from the template (return type 'int')

What I actually want is to have only a method with the specific given type in World. That means when I want to "magically" create a method based on the template, I want to sort of copy-paste the template function into the class but with the given type.

For example:

class World
public:
 World();
 ~World();

 //The magically created function with T equal to int
 int getT()
 int result;
 return result;
 

Then of course I expect to be able to call the function:

int main()
 World world; //Create world object
 world.getT<int>; //Call the function
 return 0;

Even though here I say I would call it with getT<int>, it could be only getT() (if it is a perfect copy-paste of the template function).

Be carfull

template<typename T>
T& getT() 
 T result;
 return result;

Will return a reference to a temporary. Please do

template<typename T>
T getT() 
 T result;
 return result;

without "&"

And if it's just for get a specific member, you can use std::tuple.

https://en.cppreference.com/w/cpp/utility/tuple/get

getT<int>; //"Magically" create new function from the template (return type 'int')

I don't think that will work.

It appears as though you would like to be able to use templates like macro expansion. Unfortunately, they are very different things and templates don't work like macro expansion.

However, you can use something like the following:

template<typename T>
struct GetHelper

 T get()
 
 return T;
 
;


class World : private GetHelper<int>,
 private GetHelper<double>

 public:
 World() 
 ~World() 
 template <typename T>
 get()
 
 return static_cast<GetHelper<T>*>(this)->get();
 

;

Now you can use:

World w;
int a = w.get<int>();
double b = w.get<double>();

You may also hide GetHelper as a private type of World as:

class World 

 private:
 template<typename T>
 struct GetHelper
 
 T get()
 
 return T;
 
 ;

 struct Data : GetHelper<int>,
 GetHelper<double>;

 Data data;

 public:
 World() 
 ~World() 
 template <typename T>
 get()
 
 return static_cast<GetHelper<T>*>(&data)->get();
 

;