Making a friend of a template class function

[eNergizer]

How do I make a friend out of this template function?

template <class T> class Handle
{
public:
	Handle(): p(0) { }
	Handle(const Handle& s): p(0) { if (s.p) p = s.p->clone(); }
	Handle(T* t): p(t) { }
	Handle& operator=(const Handle&);
	~Handle() { delete p; }

	operator bool() const { return p; }
	T& operator*() const;
	T* operator->() const;

private:
	T* p;
};

Is

friend class Handle;

sufficient enough? Or what do I do?

[ne555]

That will be a lot of friends.
I don't think you could. You will need to specialize Handle (or templatize the other class).

Edit: I think that I misread it. Where do you pretend to use the friendship?

[eNergizer]

So how do I specialize it? Like this?
friend class Handle<Core>;

I get a syntax error for the '<'.

Here's where I'm adding the friendship:

#ifndef GUARD_Core_h

#define GUARD_Core_h

#include <iostream>
#include <string>
#include <vector>

class Core
{
	// Friends
	friend double grade(const Core&);
	friend class Student_info;
	friend class Handle<Core>;
public:
	// Constructors
	Core(): midterm(0), final(0) { }
	Core(std::istream& is) { read(is); }
	// Virtual destructor
	virtual ~Core() {}
	// Virtual functions
	virtual std::istream& read(std::istream&);
	virtual double grade() const;
	/*Virtual function: If the argument is a Grad object,
	it will run the Grad::grade function; if the argument is a Core object, it will run the Core::grade
	function.*/
	/*This run-time selection of the virtual function to execute is relevant only when the function is called
	through a reference or a pointer.*/
	/*In contrast, a reference or pointer
	to a base-class object may refer or point to a base-class object, or to an object of a type derived
	from the base class, meaning that the type of the reference or pointer and the type of the object to
	which a reference or pointer is bound may differ at run time. It is in this case that the virtual
	mechanism makes a difference.*/

	std::string name() const;
	bool valid() const { return !homework.empty(); }
protected:
	virtual Core* clone() const { return new Core(*this); }
	// Accessible to derived classes
	std::istream& read_common(std::istream&);
	double midterm, final;
	std::vector<double> homework;
private:
	// Accessible only to Core or friends
	std::string n;
};

bool compare(const Core&, const Core&);
bool compare_Core_ptrs(const Core*, const Core*);
std::istream& read_hw(std::istream&, std::vector<double>&);

#endif 

[ne555]

http://publib.boulder.ibm.com/infocenter/comphelp/v8v101/index.jsp?topic=%2Fcom.ibm.xlcpp8a.doc%2Flanguage%2Fref%2Ffriends_and_templates.htm
So it could be done. You need to declare Handle before.

[eNergizer]

How do I get my class to make a template class a friend though? Like I want that any type that's used in the template function to be a friend of Core.

friend template<class T> class Handle;

Doesn't work.


I know I can search this up but I got dial-up, so please bare with me here.

[eNergizer]

I fixed it.

#ifndef GUARD_Core_h

#define GUARD_Core_h

#include <iostream>
#include <string>
#include <vector>

template<class T> class Handle;  // Had to add this to fix it

class Core
{
	// Friends
	friend double grade(const Core&);
	friend class Student_info;
	template<class T> friend class Handle;  // Had to add this to fix it
public:
	// Constructors
	Core(): midterm(0), final(0) { }
	Core(std::istream& is) { read(is); }
	// Virtual destructor
	virtual ~Core() {}
	// Virtual functions
	virtual std::istream& read(std::istream&);
	virtual double grade() const;
	/*Virtual function: If the argument is a Grad object,
	it will run the Grad::grade function; if the argument is a Core object, it will run the Core::grade
	function.*/
	/*This run-time selection of the virtual function to execute is relevant only when the function is called
	through a reference or a pointer.*/
	/*In contrast, a reference or pointer
	to a base-class object may refer or point to a base-class object, or to an object of a type derived
	from the base class, meaning that the type of the reference or pointer and the type of the object to
	which a reference or pointer is bound may differ at run time. It is in this case that the virtual
	mechanism makes a difference.*/

	std::string name() const;
	bool valid() const { return !homework.empty(); }
protected:
	virtual Core* clone() const { return new Core(*this); }
	// Accessible to derived classes
	std::istream& read_common(std::istream&);
	double midterm, final;
	std::vector<double> homework;
private:
	// Accessible only to Core or friends
	std::string n;
};

bool compare(const Core&, const Core&);
bool compare_Core_ptrs(const Core*, const Core*);
std::istream& read_hw(std::istream&, std::vector<double>&);

#endif 

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