CODEWITHSUNDEEP
c++boostboost-multi-array
cambunctious
cambunctious

Reputation: 9582

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;
}

Upvotes: 3

Views: 153

Answers (1)

Barry
Barry

Reputation: 303157

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

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

Where:

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 13.3.1.2 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.

Upvotes: 2

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