Operator-> transistency and shared_ptr

Question

I recall reading somewhere, can't recall where though, that operator-> is transient. That it will look through objects with operator-> until it find something that isn't a pointer and then running a normal operator. on that. I have however run into a problem with this,

Consider this code:

#include <boost/shared_ptr.hpp>
#include <vector>
#include <iostream>

struct Foo {
    Foo(int val) : i(val) {}
    typedef boost::shared_ptr<Foo> ptr;
    int i;
};

int main(int argc, char** argv) {
    typedef std::vector<Foo::ptr> FooVec;
    FooVec v;
    for(FooVec::iterator it = v.begin(); it != v.end(); ++it) {
        std::cout <<it->i <<std::endl;
    }
    return 0;
}

I get this error:

ptr.cpp: In function ‘int main(int, char**)’:
ptr.cpp:15:19: error: ‘class boost::shared_ptr<Foo>’ has no member named ‘i’
   std::cout <<it->i <<std::endl;

Since a boost::shared_ptr isn't a pointer. I could solve this by instead writing

std::cout <<(*it)->i <<std::endl

But I think that looks a lot worse, I tried std::shared_ptr as well but that got the same problem. Is there a nice way of solving this or am I stuck with (*it)->i ?

Answer 1

I recall reading somewhere, can't recall where though, that operator-> is transient.

Not in C++. You'll need to double-dereference as you already discovered.