From 90031fad221097c0410c342a7768dbb00a9bf522 Mon Sep 17 00:00:00 2001
From: kyleskyguo <32405872+kyleskyguo@users.noreply.github.com>
Date: Wed, 14 May 2025 15:54:54 +0800
Subject: [PATCH] hw03
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1,补充模板定义
2,使用decltype（aoto)自动推导函数返回值
3，使用using定义相加结果的类型
4，通过std::visit自动匹配lambda中的类型
5，重载+号，利用强制转换匹配d+c
这个练习重温了课堂上模板与几个容器的结合运用。
---
 main.cpp | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/main.cpp b/main.cpp
index d76cce7..b6f53c9 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3,9 +3,12 @@
 #include <variant>
 
 // 请修复这个函数的定义：10 分
-std::ostream &operator<<(std::ostream &os, std::vector<T> const &a) {
+template <class T>
+std::ostream &operator<<(std::ostream &os, std::vector<T> const &a)
+{
     os << "{";
-    for (size_t i = 0; i < a.size(); i++) {
+    for (size_t i = 0; i < a.size(); i++)
+    {
         os << a[i];
         if (i != a.size() - 1)
             os << ", ";
@@ -16,22 +19,44 @@ std::ostream &operator<<(std::ostream &os, std::vector<T> const &a) {
 
 // 请修复这个函数的定义：10 分
 template <class T1, class T2>
-std::vector<T0> operator+(std::vector<T1> const &a, std::vector<T2> const &b) {
+decltype(auto) operator+(std::vector<T1> const &a, std::vector<T2> const &b)
+{
     // 请实现列表的逐元素加法！10 分
     // 例如 {1, 2} + {3, 4} = {4, 6}
+    using T0 = decltype(a[0] + b[0]);
+    std::vector<T0> result;
+    for (size_t i = 0; i < std::min(a.size(), b.size()); i++)
+    {
+        result.push_back(a[i] + b[i]);
+    }
+    return result;
 }
 
 template <class T1, class T2>
-std::variant<T1, T2> operator+(std::variant<T1, T2> const &a, std::variant<T1, T2> const &b) {
+std::variant<T1, T2> operator+(std::variant<T1, T2> const &a, std::variant<T1, T2> const &b)
+{
     // 请实现自动匹配容器中具体类型的加法！10 分
+    return std::visit([&](auto const &x, auto const &y) -> std::variant<T1, T2>
+                      { return x + y; }, a, b);
+}
+
+template <class T1, class T2, class T3>
+std::variant<T1, T2> operator+(std::variant<T1, T2> const &a, T3 const &b)
+{
+    return a + std::variant<T1, T2>(b);
 }
 
 template <class T1, class T2>
-std::ostream &operator<<(std::ostream &os, std::variant<T1, T2> const &a) {
+std::ostream &operator<<(std::ostream &os, std::variant<T1, T2> const &a)
+{
     // 请实现自动匹配容器中具体类型的打印！10 分
+    std::visit([&](auto const &x)
+               { os << x; }, a);
+    return os;
 }
 
-int main() {
+int main()
+{
     std::vector<int> a = {1, 4, 2, 8, 5, 7};
     std::cout << a << std::endl;
     std::vector<double> b = {3.14, 2.718, 0.618};