different friend functions behaviour

Fabio Tesser fabio.tesser@gmail.com
Wed Apr 8 09:38:00 GMT 2009

Thanks for reply Ian.

The Argument Dependent Lookup should be active even inside a template class?
If I try put the friend function inside a template, g++ (version 4.3.2) 
gives me the following error:

$ cat test_template_friend_function.cpp
class test {
friend void ftest2(test x) {

template <class T>
class simple_template
void ftest3(T){

int main(int argc, char *argv[]) {
simple_template<int> a;

$ g++ test_template_friend_function.cpp
test_template_friend_function.cpp: In member function ‘void 
simple_template<T>::ftest3(T) [with T = int]’:
test_template_friend_function.cpp:18: instantiated from here
test_template_friend_function.cpp:12: error: no matching function for 
call to ‘ftest2(test)’

The same code compiles without errors with gcc version 4.2.4.
In your opinion what is the correct behavior?



On 04/07/2009 06:44 PM, Ian Lance Taylor wrote:
> Fabio Tesser <fabio.tesser@gmail.com> writes:
>> The difference between the two friend functions is that the first has
>> not any test class as argument while the second has a test class as
>> argument.
>> Is this the right behaviour?
> Yes, this is correct.  This is Argument Dependent Lookup, also known as
> Koenig lookup.
> http://en.wikipedia.org/wiki/Argument_dependent_lookup
> Ian

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