Template parameter as a friend

Question

In C++03 the following is illegal, although some compilers support it.

template <class T>
class X
{
    friend T;
};

Has this been legalized in C++11? (Sorry, didn't have time to read the draft myself, just hoping someone knows this)

[friends](http://www.stackoverflow.com/questions/tagged/friends) is for Facebook. — Ken Bloom, Jun 28 '11 at 16:48

score 13 · Accepted Answer · answered Jun 28 '11 at 16:52

13

From section §11.3, 3 in N3291:

template <typename T> class R {
  friend T;
};

R<C> rc; // class C is a friend of R<C>
R<int> Ri; // OK: "friend int;" is ignored

So it is legal in C++11.

answered Jun 28 '11 at 16:52

Praetorian

106,671
19
240
328

4

I am very glad `friend int;` is ignored :) – Armen Tsirunyan Jun 28 '11 at 17:40

score 1 · Answer 2 · edited Sep 23 '11 at 19:09

1

Yes c++0x allows template parameter to be friends.

Well, I happened to remember read it in the draft before but could not find the reference..anyways @Praetorian's answer nailed it.

edited Sep 23 '11 at 19:09

sehe

374,641
47
450
633

answered Jun 28 '11 at 16:46

Alok Save

202,538
53
430
533

score 0 · Answer 3 · answered Jul 01 '11 at 16:10

0

It is illegal in plain C++, but there is a simple workaround

template <class T>
class X
{
    private:
        class Wrapper
        {
            public:
                typedef T Type;
        };
        friend class Wrapper::Type;
};

answered Jul 01 '11 at 16:10

Frigo

1,709
1
14
32

Works on gcc but not on VC2010 and Comeau – Sumant Sep 28 '11 at 22:49
Yeah, tried it on Clang as well, didn't work :( - Apparently the standard forbids befriending typedef'd types which the GCC does not check for. However it is permitted to write `friend T;` which GCC does not recognize, but Clang does. – Frigo Sep 28 '11 at 23:27

Template parameter as a friend

3 Answers3

Linked