From cppreference.com
template<classT>structis_reference;(since C++11)std::is_reference is a
.
If T is a reference type (lvalue reference or rvalue reference), provides the member constant value equal true. For any other type, value is false.
If the program adds specializations for std::is_reference or std::is_reference_v, the behavior is undefined.
Template parameters
T - a type to check Helper variable template
template<classT>constexprboolis_reference_v=is_reference<T>::value;(since C++17)Inherited from
Member constants
value
[static]
true if T is a reference type, false otherwise
(public static member constant)Member functions
operator bool
converts the object to bool, returns value
(public member function)operator()
(C++14)
returns value
(public member function)Member types
Type Definition value_typebooltypestd::integral_constant<bool,value>Possible implementation
template<classT>structis_reference:std::false_type{};template<classT>structis_reference<T&>:std::true_type{};template<classT>structis_reference<T&&>:std::true_type{};Example
Run this code
#include<iostream>#include<type_traits>classA{};intmain(){# define REF(x) << #x " ?: " << x << '\n'std::cout<<std::boolalphaREF(std::is_reference_v<A>)REF(std::is_reference_v<A&>)REF(std::is_reference_v<A&&>)REF(std::is_reference_v<long>)REF(std::is_reference_v<long&>)REF(std::is_reference_v<long&&>)REF(std::is_reference_v<double*>)REF(std::is_reference_v<double*&>)REF(std::is_reference_v<double*&&>);# undef REF}Output:
std::is_reference_v<A> ?: false std::is_reference_v<A&> ?: true std::is_reference_v<A&&> ?: true std::is_reference_v<long> ?: false std::is_reference_v<long&> ?: true std::is_reference_v<long&&> ?: true std::is_reference_v<double*> ?: false std::is_reference_v<double*&> ?: true std::is_reference_v<double*&&> ?: true See also