Thread: VC 7.0 and templates

Why this code doesn't comile on VC 7.0? (gcc compile it)
The idea is that the Item class should have a handle to itself, but the handle type is known only by the Conteiner class (so if i'd like to chage a conteiner I dont need to chage Item)
Is any wy to solve this?

Code:

#include <list>
using namespace std;
template <class R>
class Item {
public:
	typedef typename R::I_handle handle;
	void SetHandle(handle h) {a=h;}
	handle GetHandle() {return a;}
private:
	handle a;
};
struct Item_type
{
	template <class R>
	struct I_Wrapper {
		typedef Item<R> Item;
	};
};
template <class I=Item_type>
class Container {
public:
	typedef Container<I> Self;
	typedef typename I::I_Wrapper<Self>::Item Item;
	typedef list<Item> Item_list;
	typedef typename Item_list::iterator I_handle;
	Item_list items;

};

int main()
{

	Container<> a;
	Container<>::Item i;
	Container<>::Item i1;
	i.SetHandle(i1.GetHandle());
	a.items.push_back(i);
}

i installed microsoft visual studio to but
i deleted it (by hand) it compiled nothing

{
with dev-c++ 4.0
it words

http://<br /> <a href="http://www.b....com</a><br />

Originally posted by Polymorphic OOP
The MS compiler is awful when it comes to compliance. You're better off using dev-c++ with minigw. They're free and actually work (though even minigw struggles with some templating)!

The thing is I have to do it on VC 7.0 somehow. BTW it does compile on VC 7.1 beta, but I cant wait for relese, I need this code working now.

OK I got it solved.
I've replaced MS STL with STLport, and it works.
But I still dont undestand what was a problem.

I know VC++ 6.0 does not handle template specialization correctly. Are you sure you just changed out the STL implementation to fix it and nothing else (that is strange indeed).

gg

Originally posted by Codeplug
I know VC++ 6.0 does not handle template specialization correctly. Are you sure you just changed out the STL implementation to fix it and nothing else (that is strange indeed).

gg

VC++ 6.0 Dosent compile this code at all it gives INTERNAL COMPILER ERROR I think becouse it dosent support template as template argument. But VC++ 7.0 does support. That's why I've got suprised. I don't know what can be wrong with STL. But fact is fact. I just have changed STL.

Dude, don't use that code. Its way to confusing for even me! You're probably trying to test your compiler but I bet you will never do something that complex in real-life. VC7.0 is a great compiler, never had any problems with templates with it yet (and I use them all the time).

Originally posted by Speedy5
Dude, don't use that code. Its way to confusing for even me! You're probably trying to test your compiler but I bet you will never do something that complex in real-life. VC7.0 is a great compiler, never had any problems with templates with it yet (and I use them all the time).

I'm using this code alredy
And actualy it's not as complex as it looks like. To not be confused with a such code I would suggest to read somthing about generic programming on C++.
And BTW VC 7.0 still doesn't support partial template specification which is too bad(fortunately 7.1 does support), it doesnt support export template, but it's OK nobody does and STL in VC 7.0 is far from the standart.

To expalin hos it works let me simplify the code:

Code:

#include <list>
using namespace std;
template <class R>
class Item {
public:
	typedef typename R::I_handle handle;
	void SetHandle(handle h) {a=h;}
	handle GetHandle() {return a;}
private:
	handle a;
	
};

template  < template < class > class I = Item >
class Container {
public:
	typedef Container<I> Self;
	typedef typename I<Self> Item;
	typedef list<Item> Item_list;
	typedef typename Item_list::iterator I_handle;
	Item_list items;

};

int main()
{

	Container<> a;
	Container<>::Item i;
	Container<>::Item i1;
	i.SetHandle(i1.GetHandle());
	a.items.push_back(i);
}

So we get rid of Wrapper, but get a template as template param
The type dependencies contain a cycle; the item type need a template argument that tells it the handle type. The Container knows the handle type and can be used as the actual type for the template argument of the item type, even though the handles have not been defined at this point. However, it is the difference between declaration and definition that allows us to use the declared type of the Container for the item type instantiation.
With respect to this instantiation the idea of this code is simuliar to Curiously Recurring Template Pattern:

Code:

template <class T>
class Base
{
	.......
};
class Curious:public Base<Curious>
{
	........
};