cambunctious cambunctious - 1 year ago 119
C++ Question

arrow operator and boost multiarray iterator

Is the arrow operator missing from boost multiarray iterators? Am I wrong to expect this to work?

#include <vector>
#include <boost/multi_array.hpp>

struct foo {
int n;

int main()
std::vector<foo> a;
auto it = a.begin();
int test = it->n; // this does compile

boost::multi_array<foo, 1> a;
auto it = a.begin();
int test = it->n; // this does not compile
return 0;

Answer Source

Seems like a bug. array_iterator::operator-> returns a:

// reference here is foo&
operator_arrow_proxy<reference> operator->() const;


template <class T>
struct operator_arrow_proxy
  operator_arrow_proxy(T const& px) : value_(px) {}
  T* operator->() const { return &value_; }
  // This function is needed for MWCW and BCC, which won't call operator->
  // again automatically per para 8
  operator T*() const { return &value_; }
  mutable T value_;

But T* here would be foo&* and you can't take a pointer to a reference. Moreover you cannot have a mutable reference member. So this whole class template is just broken for this use case.

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