#include <vector>

using namespace std;

template<typename T, typename = decltype(&T::size)>
void f1(T)
{}

template<typename T, typename = decltype(&T::size)>
void f2(T&)
{}

template<typename T, typename = decltype(&T::size)>
void f3(T&&)
{}

int main()
{
    vector<int> coll;

    f1(coll); // ok
    f2(coll); // ok
    f3(coll); // error : no matching function for call to 'f3'
}

template<typename T, typename = decltype(&std::remove_reference_t<T>::size)>
void f3(T&&)
{}

#include <vector>
#include <type_traits>

using namespace std;

template<typename T, typename = decltype(&T::size)>
void f1(T)
{}

template<typename T, typename = decltype(&T::size)>
void f2(T&)
{}

template<typename T, typename = decltype(&std::remove_reference_t<T>::size)>
void f3(T&&)
{}

int main()
{
    vector<int> coll;

    f1(coll); // ok
    f2(coll); // ok
    f3(coll); // ok
}

#include <vector>

template<typename T>
void foo(T&&){
    T nV = {3, 5, 6};
}

int main(){
    std::vector<int> Vec{1, 2 ,3, 4};
    foo(Vec);
}

#include <vector>

template<typename T>
void foo(T&&){
    using RemovedReferenceT = std::remove_reference_t<T>;
    RemovedReferenceT nV = {3, 5, 6};
}

int main(){
    std::vector<int> Vec{1, 2 ,3, 4};
    foo(Vec);
}

#include <vector>

template<typename T>
void foo(T&&){
    using RemovedReferenceT = std::remove_reference_t<T>;
    RemovedReferenceT nV = {3, 5, 6};
    nV[2] = 7;                               //woopsie
}

int main(){
    const std::vector<int> Vec{1, 2 ,3, 4};  //note the const
    foo(Vec);
}

#include <vector>

template<typename T>
void foo(T&&){
    using RRT = std::remove_reference_t<T>;
    using Removed_CV_of_RRT = std::remove_cv_t<RRT>;

    Removed_CV_of_RRT nV = {3, 5, 6};
    nV[2] = 7;
}

int main(){
    const std::vector<int> Vec{1, 2 ,3, 4};
    foo(Vec);
}