What's the point of std::remove_reference

Question

Let me dive in C++14 generic lambdas with:

#include <iostream>

// g++ -std=c++14 

template<typename T>
T incr(T v)
{
    return v + 1;
}


int main()
{
    float f = 2.0;
    int i = 3;

    auto selfincr = [] (auto & value)
        {
            value = incr<std::remove_reference<decltype(value)>>(value);    // A
            value = incr<decltype(value)>(value);                           // B
        };


    selfincr(f);
    selfincr(i);

    std::cout << "f " << f << ", i " << i << std::endl;
    return 0;
}

Since line // B causes a

invalid initialization of non-const reference of type ‘T&’ from an rvalue of type ‘T’

My immediate guessing has been the removal of the reference, so I added line // A. But this yield a

no matching function for call to ‘incr(T&)’

So how could I remove that reference ?

Answer 1

So how could I remove that reference ?

incr<std::remove_reference<decltype(value)>>(value), you're specifying std::remove_reference<T> as the template parameter, but not the type referred by T (i.e. decltype(value)). What you want should be

value = incr<typename std::remove_reference<decltype(value)>::type>(value);    // A
//           ~~~~~~~~                                       ~~~~~~        

And since C++14 you could make it simpler:

value = incr<std::remove_reference_t<decltype(value)>>(value);    // A
//                                ~~ 

LIVE