boost::phoenix error message while used as a functor - c++

Question

I am trying to learn boost::phoenix and trying to use it in std::transform like below.
class myClass
{
int i;
public:
getNumber();
setNumber(int j);
};
int main()
{
std::vector<myClass*> vect
std::vector<int> numVect
numVect.resize(vect.size());
using boost::phoenix::arg_names::arg1;
std::transform (vect.begin(), vect.end(), numVect.begin(), arg1->getNumber());
}
But, I am getting an error error: base operand of '->' has non-pointer type 'const boost::phoenix::actor<boost::phoenix::argument<0> >'
I am not really sure what does it mean. Any help would be great. Thanks

Answer 1

As you note above, the way to do this with Phoenix is with phoenix::bind or with ->* as you do above:
#include <vector>
#include <boost/phoenix/core.hpp>
#include <boost/phoenix/operator.hpp>
#include <boost/range/algorithm/transform.hpp>
class myClass
{
int i;
public:
int getNumber() { return i; }
void setNumber(int j) { i = j; }
};
int main()
{
std::vector<myClass*> vect;
std::vector<int> numVect;
using boost::phoenix::arg_names::arg1;
boost::transform(vect,
std::back_inserter(numVect),
(arg1->*&myClass::getNumber)());
}
Phoenix can be complicated, and bind expressions are some of the most convoluted and contrived of Phoenix's syntactic contortions, but in all honestly, this one doesn't seem that bad.
C++14's polymorphic lambdas will obviate much of Phoenix, by the way.

Answer 2

I'd use
std::transform (vect.begin(), vect.end(), numVect.begin(), phx::bind(&myClass::getNumber, arg1));
Or, if you wanted nicer syntax:
auto getNumber = phx::lambda [ phx::bind(&myClass::getNumber, arg1) ];
std::transform (vect.begin(), vect.end(), numVect.begin(), getNumber(arg1));
Demo:
#include <vector>
#include <algorithm>
#include <iostream>
#include <boost/phoenix/phoenix.hpp>
namespace phx = boost::phoenix;
struct myClass
{
int i;
int getNumber() const { return i; }
void setNumber(int j) { i = j; }
};
using namespace boost::phoenix::arg_names;
static const auto getNumber = phx::lambda [ phx::bind(&myClass::getNumber, arg1) ];
int main()
{
const std::vector<myClass*> vect { new myClass{1}, new myClass{2}, new myClass{42} };
std::vector<int> numVect(vect.size());
// puritan/standard version:
std::transform (vect.begin(), vect.end(), numVect.begin(), std::mem_fn(&myClass::getNumber));
// just bind:
std::transform (vect.begin(), vect.end(), numVect.begin(), phx::bind(&myClass::getNumber, arg1));
// using more natural syntax
std::transform (vect.begin(), vect.end(), numVect.begin(), getNumber(arg1));
for(auto i : numVect)
std::cout << i << " ";
}