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collapses.cpp
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collapses.cpp
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//
// 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.
}