- std::tuple<>預設按順序比較
- std::tie能把值引用打包
- C++20 <=>能按成員變量聲明順序比較
#include <iostream>
#include "common/log.h"
#include <limits>
#include <vector>
#include <span>
#include <array>
#include <type_traits>
#include <cmath>
#include <memory>
#include <variant>
using namespace AdsonLib;
struct Point1{
int x;
int y;
friend bool operator==(const Point1 &a, const Point1 &b);
friend bool operator<(const Point1 &a, const Point1 &b);
};
bool operator==(const Point1 &a, const Point1 &b) {
return std::tie(a.x, a.y) == std::tie(b.x, b.y);
}
bool operator<(const Point1 &a, const Point1 &b) {
return std::tie(a.x, a.y) < std::tie(b.x, b.y);
}
struct Point2{
Point2(int a, int b):x(a), y(b){}
virtual ~Point2(){}
int x;
int y;
//預設比較,按成員定義順序. 可以有虛函數
friend auto operator<=>(const Point2 &a, const Point2 &b) = default;
};
struct Point3{
int x;
int y;
//預設比較,按成員定義順序. 可以有虛函數
friend auto operator<=>(const Point3 &a, const Point3 &b);
};
auto operator<=>(const Point3 &a, const Point3 &b) {
auto v1 = a.x * a.y;
auto v2 = b.x * b.y;
return v1 - v2;
}
//偏序(partial_ordering):不是任意兩個可比較大小
//弱序(weak_ordering):任意兩個可比較大小,但是相等定義為不大于也不小于
//強序(strong_ordering):任意兩個可比較大小,也定義了相等比較
int main(int argc, char *argv[]) {
std::tuple t1(0,3);
std::tuple t2(0,2);
auto t3 = std::tuple(4,5);
auto b = (t1 <=> t3);
Point2 p20{0,1};
Point2 p21{0,2};
LOG(INFO) << "cmp: " << (t1 < t2) << " <=> " << (p20 < p21);
Point3 p30{4,1};
Point3 p31{1,2};
LOG(INFO) << (p30 > p31) << " <=> " << (p30 < p31);
}