Home/ Questions/Q 6940507
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-27T12:45:41+00:00

I am having trouble aliasing the function boost::make_iterator_range (I would like to hide boost

  • 0

I am having trouble aliasing the function boost::make_iterator_range

(I would like to hide boost behind an alias in case this particular library gets adopted into the standard sometime in the future.)

Is there any way this can be made to work?

#include <boost/range/iterator_range.hpp>

void Foo()
{
}

template< typename T >
void Bar()
{ }

template< typename T >
void Bar(char c)
{ }

void (&FooAlias)() = Foo;           // ok
void (&BarAlias)() = Bar<int>;      // ok

// boost::iterator_range<const size_t*> (&MakeIterRangeAlias)(const size_t*,const size_t*) = 
//  boost::make_iterator_range<const size_t*>;  // not ok

int main(int argc, char** argv)
{
    const size_t v[] = { 3, 5, 1, 5, 29, 15 };

    boost::iterator_range<const size_t*> r 
        = boost::make_iterator_range( std::begin( v ), std::end( v )); // want to alias this

    return 0;
}

The error message is:

In file included from /usr/include/boost/iterator/iterator_categories.hpp:15:0,
                 from /usr/include/boost/iterator/detail/facade_iterator_category.hpp:7,
                 from /usr/include/boost/iterator/iterator_facade.hpp:14,
                 from /usr/include/boost/range/iterator_range_core.hpp:23,
                 from /usr/include/boost/range/iterator_range.hpp:13,
                 from sandbox.cpp:2:
/usr/include/boost/mpl/eval_if.hpp: In instantiation of ‘boost::mpl::eval_if_c<true, boost::range_const_iterator<const long unsigned int*>, boost::range_mutable_iterator<const long unsigned int* const> >’:
/usr/include/boost/range/iterator.hpp:63:63:   instantiated from ‘boost::range_iterator<const long unsigned int* const>’
sandbox.cpp:20:10:   instantiated from here
/usr/include/boost/mpl/eval_if.hpp:60:31: error: no type named ‘type’ in ‘boost::mpl::eval_if_c<true, boost::range_const_iterator<const long unsigned int*>, boost::range_mutable_iterator<const long unsigned int* const> >::f_ {aka struct boost::range_const_iterator<const long unsigned int*>}’
/usr/include/boost/mpl/eval_if.hpp: In instantiation of ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<const long unsigned int*>, boost::range_mutable_iterator<const long unsigned int*> >’:
/usr/include/boost/range/iterator.hpp:63:63:   instantiated from ‘boost::range_iterator<const long unsigned int*>’
sandbox.cpp:20:10:   instantiated from here
/usr/include/boost/mpl/eval_if.hpp:60:31: error: no type named ‘type’ in ‘boost::mpl::eval_if_c<false, boost::range_const_iterator<const long unsigned int*>, boost::range_mutable_iterator<const long unsigned int*> >::f_ {aka struct boost::range_mutable_iterator<const long unsigned int*>}’
sandbox.cpp:20:10: error: invalid initialization of non-const reference of type ‘void (&)(const size_t*, const size_t*) {aka void (&)(const long unsigned int*, const long unsigned int*)}’ from an rvalue of type ‘<unresolved overloaded function type>’
make: *** [sandbox] Error 1
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Using function pointers is a suboptimal way alias a function. It is not as flexible as the original (it can no longer be a template) and you now need to know the exact signature of the function, which may or may not be stable.
    Instead try this approach.

    template< typename ... Args >
auto MakeIterRangeAlias( Args&& ... args ) -> decltype( /* copy return line here */ )
{
   return boost::make_iterator_range( std::forward<Args>(args)... );
}

    With almost no work on your part the alias supports the exact signature of the original. Even if it dramatically changes, you’re still set. Further, unlike the function pointer approach the optimizer will be able to trivially inline MakeIterRangeAlias so that there is no runtime overhead.

    • 0