R.34-35 shared_ptr examples (#1808)

CppCoreGuidelines.md

@@ -9135,7 +9135,7 @@ Here, we ignore such cases.
   * [R.31: If you have non-`std` smart pointers, follow the basic pattern from `std`](#Rr-smart)
   * [R.32: Take a `unique_ptr<widget>` parameter to express that a function assumes ownership of a `widget`](#Rr-uniqueptrparam)
   * [R.33: Take a `unique_ptr<widget>&` parameter to express that a function reseats the `widget`](#Rr-reseat)
-  * [R.34: Take a `shared_ptr<widget>` parameter to express that a function is part owner](#Rr-sharedptrparam-owner)
+  * [R.34: Take a `shared_ptr<widget>` parameter to express shared ownership](#Rr-sharedptrparam-owner)
   * [R.35: Take a `shared_ptr<widget>&` parameter to express that a function might reseat the shared pointer](#Rr-sharedptrparam)
   * [R.36: Take a `const shared_ptr<widget>&` parameter to express that it might retain a reference count to the object ???](#Rr-sharedptrparam-const)
   * [R.37: Do not pass a pointer or reference obtained from an aliased smart pointer](#Rr-smartptrget)
@@ -9810,7 +9810,7 @@ Using `unique_ptr` in this way both documents and enforces the function call's r
 * (Simple) Warn if a function takes a `Unique_pointer<T>` parameter by lvalue reference and does not either assign to it or call `reset()` on it on at least one code path. Suggest taking a `T*` or `T&` instead.
 * (Simple) ((Foundation)) Warn if a function takes a `Unique_pointer<T>` parameter by reference to `const`. Suggest taking a `const T*` or `const T&` instead.
 
-### <a name="Rr-sharedptrparam-owner"></a>R.34: Take a `shared_ptr<widget>` parameter to express that a function is part owner
+### <a name="Rr-sharedptrparam-owner"></a>R.34: Take a `shared_ptr<widget>` parameter to express shared ownership
 
 ##### Reason
 
@@ -9818,11 +9818,16 @@ This makes the function's ownership sharing explicit.
 
 ##### Example, good
 
-    void share(shared_ptr<widget>);            // share -- "will" retain refcount
-
-    void may_share(const shared_ptr<widget>&); // "might" retain refcount
-
-    void reseat(shared_ptr<widget>&);          // "might" reseat ptr
+    class WidgetUser
+    {
+    public:
+        // WidgetUser will share ownership of the widget
+        explicit WidgetUser(std::shared_ptr<widget> w) noexcept:
+            m_widget{std::move(w)} {}
+        // ...
+    private:
+        std::shared_ptr<widget> m_widget;
+    };
 
 ##### Enforcement
 
@@ -9842,11 +9847,11 @@ This makes the function's reseating explicit.
 
 ##### Example, good
 
-    void share(shared_ptr<widget>);            // share -- "will" retain refcount
-
-    void reseat(shared_ptr<widget>&);          // "might" reseat ptr
-
-    void may_share(const shared_ptr<widget>&); // "might" retain refcount
+    void ChangeWidget(std::shared_ptr<widget>& w)
+    {
+        // This will change the callers widget
+        w = std::make_shared<widget>(widget{});
+    }
 
 ##### Enforcement
 

scripts/hunspell/isocpp.dic

@@ -646,6 +646,7 @@ webby
 Webcolor
 webcolors
 WG21
+WidgetUser
 WorkQueue
 'widen'
 x1