54 lines
1.3 KiB
C++
54 lines
1.3 KiB
C++
//
|
||
// Created by light on 19-12-15.
|
||
//
|
||
#include <iostream>
|
||
|
||
using namespace std;
|
||
|
||
template<typename T>
|
||
void f(T &¶m) {
|
||
static_assert(std::is_lvalue_reference<T>::value, "T& is lvalue reference");
|
||
cout << "T& is lvalue reference" << endl;
|
||
}
|
||
|
||
template<typename T>
|
||
class Widget {
|
||
typedef T& LvalueRefType;
|
||
typedef T&& RvalueRefType;
|
||
public:
|
||
void judge() {
|
||
static_assert(std::is_lvalue_reference<LvalueRefType>::value, "LvalueRefType & is lvalue reference");
|
||
static_assert(std::is_lvalue_reference<RvalueRefType>::value, "RvalueRefType & is lvalue reference");
|
||
cout << "LvalueRefType and RvalueRefType is lvalue reference" << endl;
|
||
}
|
||
void f(LvalueRefType&& param) {
|
||
|
||
}
|
||
};
|
||
|
||
|
||
int main() {
|
||
int x;
|
||
int &&r1 = 10;
|
||
int &r2 = x;
|
||
f(r1);
|
||
f(r2);
|
||
|
||
Widget<int &> w;
|
||
w.judge();
|
||
|
||
|
||
Widget<int> w1, w2;
|
||
|
||
auto&& v1 = w1; // v1 is an auto-based universal reference being
|
||
// initialized with an lvalue, so v1 becomes an
|
||
// lvalue reference referring to w1.
|
||
|
||
// 不能编译
|
||
// decltype(w1)&& v2 = w2; // v2 is a decltype-based universal reference, and
|
||
// decltype(w1) is Widget, so v2 becomes an rvalue reference.
|
||
// w2 is an lvalue, and it’s not legal to initialize an
|
||
// rvalue reference with an lvalue, so
|
||
// this code does not compile.
|
||
}
|