[Bug c++/22363] New: Problems with friend function injection and destructor

[Bug c++/22363] New: Problems with friend function injection and destructor

[cxl at ntllib dot org]

This code does not compile:

template <class T>
struct Feature {
	friend void AssertFeature0(T *) {}
};

template <class T>
inline void AssertFeature(T *t = 0) { if(t) AssertFeature0(t); }

template <class T>
struct Test : Feature< Test<T> >
{
	int i;
	~Test() { AssertFeature<T>(); }
};

struct Foo : Feature<Foo> { int x; };

void foo()
{
	Test< Test<Foo> > test;
}

----------------------
The problem seems to be in fact that ~Test destructor is instantiated BEFORE
friend is injected and only in the case that templates are nested. Moving
AssertFeature to other method (and instatiating) or reducing test-case to just
"Test<Foo> test;" makes code compile fine.

Comeau C++ testdrive compiles this code without problems.

-- 
           Summary: Problems with friend function injection and destructor
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cxl at ntllib dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363

[Bug c++/22363] Problems with friend function injection and destructor

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2005-07-08 14:19 -------
*** Bug 22364 has been marked as a duplicate of this bug. ***

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363

[Bug c++/22363] Problems with friend function injection and destructor

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
      Known to fail|                            |2.95.3 3.2.3 3.3.3 3.4.0
                   |                            |4.0.0 3.0.4 4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363

[Bug c++/22363] Problems with friend function injection and destructor

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2005-07-08 14:58 -------
I don't quite know what to say, whether this is a bug or not. Take 
this reduced snippet: 
--------------------------- 
template <class T> struct S { 
    friend void foo(T *); 
}; 
 
template <class T> void bar() { foo((T*)0); } 
 
template <class T> 
struct X : S< X<T> > 
{ 
    X() { bar<T>(); } 
}; 
 
X< X<int> > test; 
---------------------------- 
icc compiles this, but gcc doesn't, with this error message: 
 
g/x> /home/bangerth/bin/gcc-4.1*/bin/c++ -c x.cc 
x.cc:2: warning: friend declaration &#8216;void foo(T*)&#8217; declares a non-template 
function 
x.cc:2: warning: (if this is not what you intended, make sure the function 
template has already been declared and add <> after the function name here) 
-Wno-non-template-friend disables this warning 
x.cc: In function &#8216;void bar() [with T = X<int>]&#8217;: 
x.cc:10:   instantiated from &#8216;X<T>::X() [with T = X<int>]&#8217; 
x.cc:13:   instantiated from here 
x.cc:5: error: cannot convert &#8216;X<int>*&#8217; to &#8216;X<X<int> >*&#8217; for argument &#8216;1&#8217; to 
&#8216;void foo(X<X<int> >*)&#8217; 
 
What is happening is that in the definition of 'test', we instantiate 
X<X<int> >, which through its derivation from S<X<X<int>>> makes sure  
that there is a function foo<X<X<int>>> (that this function is available 
is visible from the error message). However, in the destructor of 
X<X<int>>, we call bar<X<int>> which in turn wants to call foo<X<int>>, 
which doesn't exist. 
 
I believe that the reason why icc can compile this is that in the definition 
of 'test', the compiler does not only instantiate X<X<int>>, but also X<int>. 
If that were the case, then we would have a function foo<X<int>> from that 
instantiation, available for use when we get to instantiate the destructor 
of X<X<int>>. The question is: do we need to instantiate X<int> in order to 
instantiate X<X<int>>? 
 
(Here's a sidenote: apparently, icc only instantiates the *type* X<int>, 
but not the destructor X<int>::~X. I can infer this because if it did, 
then it would want to call bar<int> which in turn would want to call 
foo<int>; that one, however, doesn't exist...) 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363

[Bug c++/22363] Problems with friend function injection and destructor

[pinskia at gcc dot gnu dot org]

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------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-30 05:12 -------
For the testcase in comment #2, on the mainline, we get a different error message:

t.cc:2: warning: friend declaration ‘void foo(T*)’ declares a non-template function
t.cc:2: warning: (if this is not what you intended, make sure the function template has already been 
declared and add <> after the function name here) -Wno-non-template-friend disables this warning
t.cc: In function ‘void bar() [with T = X<int>]’:
t.cc:10:   instantiated from ‘X<T>::X() [with T = X<int>]’
t.cc:13:   instantiated from here
t.cc:5: error: ‘foo’ was not declared in this scope

This seems better as friend don't intject the declation at all.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363

[Bug c++/22363] Problems with friend function injection and destructor

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2006-10-21 20:23 -------
(In reply to comment #3)
> For the testcase in comment #2, on the mainline, we get a different error
> message:

That is the correct error so closing as fixed for 4.2.0 as friends don't inject
at all.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22363