vault backup: 2022-06-08 10:55:41

Affected files:
.obsidian/workspace
02. PARA/03. Resources（資源）/C++17/rvalue.md

.obsidian/workspace

@@ -10,7 +10,7 @@
         "state": {
           "type": "markdown",
           "state": {
-            "file": "00. TOP/01. TODO.md",
+            "file": "02. PARA/03. Resources（資源）/C++17/rvalue.md",
             "mode": "source",
             "source": true
           }
@@ -23,7 +23,7 @@
         "state": {
           "type": "outline",
           "state": {
-            "file": "00. TOP/01. TODO.md"
+            "file": "02. PARA/03. Resources（資源）/C++17/rvalue.md"
           }
         }
       }
@@ -81,7 +81,7 @@
             "state": {
               "type": "backlink",
               "state": {
-                "file": "00. TOP/01. TODO.md",
+                "file": "02. PARA/03. Resources（資源）/C++17/rvalue.md",
                 "collapseAll": true,
                 "extraContext": true,
                 "sortOrder": "alphabetical",
@@ -125,6 +125,7 @@
   },
   "active": "94f0e8a81af6c9e2",
   "lastOpenFiles": [
+    "02. PARA/03. Resources（資源）/C++17/rvalue.md",
     "00. TOP/01. TODO.md",
     "02. PARA/01. Project（專案）/008. Sentinel.md",
     "02. PARA/03. Resources（資源）/FFMPEG/01. Setup.md",
@@ -133,7 +134,6 @@
     "02. PARA/03. Resources（資源）/99. templates/日記.md",
     "01. Daily/2022-06-06(週一).md",
     "02. PARA/03. Resources（資源）/Qt.md",
-    "02. PARA/03. Resources（資源）/C++17/智慧指標.md",
+    "02. PARA/03. Resources（資源）/C++17/智慧指標.md"
-    "02. PARA/04. Archives（歸檔）/01. Project（專案）/004. Group firmware update check.md"
   ]
 }

02. PARA/03. Resources（資源）/C++17/rvalue.md

@@ -1,9 +1,18 @@
 - 等號右邊的值
 - 臨時的值，例如運算的結果
+- 無法被取址（address-of）的物件
 
 # rvalue參考
-可以用兩個`&`來參考rvalue。例如：
+可以用`&&`來參考rvalue。例如：
 ```
 int c{5};
 int&& rtepm {c + 3};
 ```
+
+關於lvalue、rvalue的分別可以參考[Value categories - cppreference.com](https://en.cppreference.com/w/cpp/language/value_category)，或是[rvalue 參考](https://openhome.cc/Gossip/CppGossip/RvalueReference.html)等文章。這邊講用法跟好處。
+rvalue reference可以減少無間的複製成本。例如：
+```cpp
+std::string longStr = "qwertyuiopasdfghjklzxcbnm";
+std::string anotherLong = longStr;
+```
+這時longStr會被複製一份anotherLong，把longStr換成很大的buffer，