From: "Duane Murphy"
I am trying to make a member function call to all objects returned by an
iterator. mem_fn is giving me an error when trying to call get_pointer()
for a reference object. There is no overload for get_pointer of a
reference object. Is there some reason or should I be doing this
differently.
[...]
Here is some pseudo code to get things in the right orientation.
class obj
{
public:
void method();
};
class obj_iterator
{
public:
obj& iterator::operator*() const { return obj_; }
};
class obj_container
{
public:
obj_iterator begin();
obj_iterator end();
}
{
...
obj_container c;
foreach( c.begin(), c.end(), mem_fn( method ) );
}
Your code works, when modified appropriately. mem_fn recognizes obj&
references.
The following modification, however, does not work (which might be your
problem):
#include
#include <algorithm>
class obj_base
{
public:
void method();
};
class obj: public obj_base
{
};
class obj_iterator
{
public:
obj& operator*() const;
obj_iterator & operator++();
};
bool operator==(obj_iterator, obj_iterator);
bool operator!=(obj_iterator, obj_iterator);
class obj_container
{
public:
obj_iterator begin();
obj_iterator end();
};
int main()
{
obj_container c;
std::for_each( c.begin(), c.end(), boost::mem_fn( &obj::method ) );
}
&obj::method is actually of type void (obj_base::*) (), and while mem_fn
recognizes references to the 'base' type (obj_base&), it cannot tell whether
obj& is a smart pointer or an object reference.
I can probably fix this by using boost::is_convertible but
unfortunately it's known to break some compilers. Food for thought. Thanks
for the bug report. :-)
--
Peter Dimov
Multi Media Ltd.
