Re: [Boost-users] transform_iterator and c++11 lambda expression

Subject: Re: [Boost-users] transform_iterator and c++11 lambda expression
From: paul Fultz (pfultz2_at_[hidden])
Date: 2012-09-21 22:15:27

I use this wrapper:

    #define RETURNS(...) -> decltype(__VA_ARGS__) { return (__VA_ARGS__); }

    template<class Fun>
    struct function_object
    {
        boost::optional<Fun> f;

        function_object()
        {}
        function_object(Fun f): f(f)
        {}

        function_object(const function_object & rhs) : f(rhs.f)
        {}

        // Assignment operator is just a copy construction, which does not provide
        // the strong exception guarantee.
        function_object& operator=(const function_object& rhs)
        {
            if (this != &rhs)
            {
                this->~function_object();
                new (this) function_object(rhs);
            }
            return *this;
        }

        template<class F>
        struct result
        {};

        template<class F, class T>
        struct result<F(T)>
        {
            typedef decltype(std::declval<Fun>()(std::declval<T>())) type;
        };

        template<class T>
        auto operator()(T && x) const RETURNS((*f)(std::forward<T>(x)))

        template<class T>
        auto operator()(T && x) RETURNS((*f)(std::forward<T>(x)))
    };

    template<class F>
    function_object<F> make_function_object(F f)
    {
        return function_object<F>(f);
    }

Then you can create the transform iterator like this:

    boost::make_transform_iterator(my_itertor, make_function_object([](int& i) { return i + 1; }));




----- Original Message -----
> From: MM <finjulhich_at_[hidden]>
> To: Boost-users_at_[hidden]
> Cc: 
> Sent: Friday, September 21, 2012 6:37 PM
> Subject: [Boost-users] transform_iterator and c++11 lambda expression
> 
> hello
> it would be great to be pass
> 
> transform_iterator( my_iterator, []( reference ) {  return /// something } );
> 
> directly to STL algorithms.
> 
> Currently, one needs to define separately the unarfy function as far
> as i could see
> 
> MM
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