Re: [Boost-users] boost::transform_iterator, boost::array::iterator and category

Subject: Re: [Boost-users] boost::transform_iterator, boost::array::iterator and category
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-04-03 17:40:20

AMDG

Hicham Mouline wrote:
> typedef transform_iterator< UnaryFunction, ... >   iteratorIntoFirst;
>
>
> struct UnaryFunction: public std::unary_function< pair<double, double>,
> double> {
>     double operator()( const pair<double, double>& e ) const
>     {
>       return e.first;
>     }
>   }
>
> However on asserting the category is still random access, boost static
> assert fails:
> <snip>
>   

Try returning a reference const double& instead of double.

struct UnaryFunction {
    typedef const double& result_type;
    const double& operator()( const pair<double, double>& e ) const
    {
        return e.first;
    }
};

Random access iterators must return an lvalue.

In Christ,
Steven Watanabe