Re: making friends with static members of template arguments
Oncaphillis wrote:
Hi,
I'm trying to make friends with static member functions
of template arguments:
<snip>
#include <iostream>
class some_policy {
public:
template<class FooT>
static void bar(const FooT *f) {
std::cerr << f->a;
}
};
template<class PolicyT>
class foo {
public:
foo() : a(33) {
}
void bar() {
PolicyT::bar(this);
}
protected:
int a;
friend
void PolicyT::bar< foo >(const foo *);
};
int main() {
foo<some_policy> f;
f.bar();
}
</snip>
So the idea is to specialize some behavior of the foo class in
class PolicyT which itself contains template static member
functions depending on the concrete foo class. I do not want
to make the whole PolicyT a template class since other static
member functions should only depend on some other internal
types of foo (kind of a replacement of partial template
specialization of foo members).
Everything works fine whenever I make 'int a' public and leave
out the 'friend..' part, but making the PolicyT::bar< foo>(...) a
friend fails
g++ 4.1.2 tells me
<snip>
test.cc:26: error: type ?PolicyT? is not derived from type ?foo<PolicyT>?
test.cc:26: error: expected ?;? before ?<? token
</snip>
Hmm... that's not very enlightening. Am I on the totally wrong trip
here or just in search for the proper syntax ?
http://www.comeaucomputing.com/techtalk/templates/#friendclassT
I can't find exact information for your problem
But I think these are quite the same,
allowing "friend T;" or friend "void T::foo(...);" violates the
encapsulation, as client programmer can define his own class or policy
function to access private/protected data.
--
Best Regards
Barry
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