indirected range adaptor not satisfied with unary dereference operator

[Lars Viklund <zao@…>]

The documentation for Range's indirected adaptor claims that it is usable with anything that has an unary operator*().

When using it with a range of optional<int>, it seems to require an element_type inner type, which optional doesn't expose and the docs does not require.

The following testcase fails to compile with VC10 and GCC 4.2.3:

#include <boost/optional.hpp>
#include <boost/range/adaptors.hpp>
#include <vector>

int main(int argc, char* argv[])
{
        std::vector<boost::optional<int> > v;
        v | boost::adaptors::indirected;
}

[Lars Viklund <zao@…>]

This was apparently known back in May in a ​question on Stack Overflow, which also mentions a workaround for Boost.Optional. It doesn't address the underlying doc bug though, so the ticket is still valid.

#include <boost/optional/optional_fwd.hpp>
#include <boost/pointee.hpp>

namespace boost
{
    template<typename P>
    struct pointee<optional<P> >
    {
        typedef typename optional<P>::value_type type;
    };
}

[Júlio Hoffimann Mendes <julio.hoffimann@…>]

I found this related topic on stackoverflow:

​http://stackoverflow.com/questions/6123327/use-boostoptional-together-with-boostadaptorsindirected

The first answer solved the problem for me, i don't know if it's safe though.

Regards, Júlio.

[Neil Groves]

Added a unit test to confirm that a fix has been made to Boost.Optional and that the use-case now works as expected when using optional with the indirected adapter.

[rob.desbois@…]

This doesn't appear to be fixed; I've tried the testcase using the latest Boost (1.65.1) with both clang 4.01 and gcc 6.4.1, but still get the compilation failure:

boost_1_65_1/boost/pointee.hpp:30:27: error: no type named 'element_type' in 'boost::optional<int>'