feat: add reference type traits (#19)

Author: jyxiong

source/tinystl/type_traits/composite_type_categories/is_reference.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include "tinystl/type_traits/primary_type_categories/is_lvalue_reference.h"
+#include "tinystl/type_traits/primary_type_categories/is_rvalue_reference.h"
+
+namespace tinystl {
+template<class T>
+struct is_reference : bool_constant<is_lvalue_reference<T>::value || is_rvalue_reference<T>::value> {};
+
+template <class T>
+inline constexpr bool is_reference_v = is_reference<T>::value;
+}

source/tinystl/type_traits/primary_type_categories/is_lvalue_reference.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "tinystl/type_traits/helper_classes/integral_constant.h"
+
+namespace tinystl {
+template<class T>
+struct is_lvalue_reference : false_type {};
+template<class T>
+struct is_lvalue_reference<T&> : true_type {};
+
+template<class T>
+inline constexpr bool is_lvalue_reference_v = is_lvalue_reference<T>::value;
+}

source/tinystl/type_traits/primary_type_categories/is_rvalue_reference.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "tinystl/type_traits/helper_classes/integral_constant.h"
+
+namespace tinystl {
+template<class T>
+struct is_rvalue_reference : false_type {};
+template<class T>
+struct is_rvalue_reference<T&&> : true_type {};
+
+template <class T>
+inline constexpr bool is_rvalue_reference_v = is_rvalue_reference<T>::value;
+}