Add reference_cycles example

.idea/misc.xml

@@ -27,6 +27,7 @@
     <cargoProject FILE="$PROJECT_DIR$/smart_pointers/Cargo.toml" />
     <cargoProject FILE="$PROJECT_DIR$/reference_counting/Cargo.toml" />
     <cargoProject FILE="$PROJECT_DIR$/interior_mutability/Cargo.toml" />
+    <cargoProject FILE="$PROJECT_DIR$/reference_cycles/Cargo.toml" />
   </component>
   <component name="ComposerJsonPluginSettings">
     <unboundedVersionInspectionSettings>

.idea/rust.iml

@@ -110,6 +110,10 @@
       <sourceFolder url="file://$MODULE_DIR$/interior_mutability/examples" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/interior_mutability/tests" isTestSource="true" />
       <sourceFolder url="file://$MODULE_DIR$/interior_mutability/benches" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/reference_cycles/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/reference_cycles/examples" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/reference_cycles/tests" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/reference_cycles/benches" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/add/add-one/target" />
       <excludeFolder url="file://$MODULE_DIR$/add/adder/target" />
       <excludeFolder url="file://$MODULE_DIR$/adder/target" />
@@ -130,6 +134,7 @@
       <excludeFolder url="file://$MODULE_DIR$/modules/target" />
       <excludeFolder url="file://$MODULE_DIR$/rectangles/target" />
       <excludeFolder url="file://$MODULE_DIR$/reference_counting/target" />
+      <excludeFolder url="file://$MODULE_DIR$/reference_cycles/target" />
       <excludeFolder url="file://$MODULE_DIR$/references/target" />
       <excludeFolder url="file://$MODULE_DIR$/scope/target" />
       <excludeFolder url="file://$MODULE_DIR$/slices/target" />

.idea/workspace.xml

@@ -5,7 +5,6 @@
       <change beforePath="$PROJECT_DIR$/.idea/misc.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/misc.xml" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/.idea/rust.iml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/rust.iml" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/reference_counting/src/main.rs" beforeDir="false" afterPath="$PROJECT_DIR$/reference_counting/src/main.rs" afterDir="false" />
     </list>
     <option name="EXCLUDED_CONVERTED_TO_IGNORED" value="true" />
     <option name="SHOW_DIALOG" value="false" />
@@ -15,24 +14,11 @@
   </component>
   <component name="FileEditorManager">
     <leaf>
-      <file pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/interior_mutability/src/lib.rs">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="672">
-              <caret line="55" column="69" selection-start-line="55" selection-start-column="69" selection-end-line="55" selection-end-column="69" />
-              <folding>
-                <element signature="e#1104#1105#0" expanded="true" />
-                <element signature="e#1144#1145#0" expanded="true" />
-              </folding>
-            </state>
-          </provider>
-        </entry>
-      </file>
       <file pinned="false" current-in-tab="true">
-        <entry file="file://$PROJECT_DIR$/reference_counting/src/main.rs">
+        <entry file="file://$PROJECT_DIR$/reference_cycles/src/main.rs">
           <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="320">
+            <state relative-caret-position="160">
-              <caret line="20" column="15" selection-start-line="20" selection-start-column="15" selection-end-line="20" selection-end-column="15" />
+              <caret line="10" column="11" lean-forward="true" selection-start-line="10" selection-start-column="11" selection-end-line="10" selection-end-column="11" />
             </state>
           </provider>
         </entry>
@@ -108,6 +94,7 @@
         <option value="$PROJECT_DIR$/smart_pointers/src/main.rs" />
         <option value="$PROJECT_DIR$/interior_mutability/src/lib.rs" />
         <option value="$PROJECT_DIR$/reference_counting/src/main.rs" />
+        <option value="$PROJECT_DIR$/reference_cycles/src/main.rs" />
       </list>
     </option>
   </component>
@@ -141,12 +128,12 @@
             <path>
               <item name="rust" type="3d21c010:ScopeViewTreeModel$ProjectNode" />
               <item name="rust" type="2674bda8:ScopeViewTreeModel$GroupNode" />
-              <item name="reference_counting" type="9f88c78c:ScopeViewTreeModel$FileNode" />
+              <item name="reference_cycles" type="9f88c78c:ScopeViewTreeModel$FileNode" />
             </path>
             <path>
               <item name="rust" type="3d21c010:ScopeViewTreeModel$ProjectNode" />
               <item name="rust" type="2674bda8:ScopeViewTreeModel$GroupNode" />
-              <item name="reference_counting" type="9f88c78c:ScopeViewTreeModel$FileNode" />
+              <item name="reference_cycles" type="9f88c78c:ScopeViewTreeModel$FileNode" />
               <item name="src" type="9f88c78c:ScopeViewTreeModel$FileNode" />
             </path>
           </expand>
@@ -180,7 +167,7 @@
   </component>
   <component name="PropertiesComponent">
     <property name="JavaScriptWeakerCompletionTypeGuess" value="true" />
-    <property name="com.android.tools.idea.instantapp.provision.ProvisionBeforeRunTaskProvider.myTimeStamp" value="1549381304560" />
+    <property name="com.android.tools.idea.instantapp.provision.ProvisionBeforeRunTaskProvider.myTimeStamp" value="1549383008644" />
     <property name="javascript.nodejs.core.library.configured.version" value="7.1.0" />
     <property name="js.eslint.eslintPackage" value="$USER_HOME$/.yarn-config/global/node_modules/.bin/eslint" />
     <property name="js.eslint.nodeInterpreter" value="project" />
@@ -208,7 +195,7 @@
       </list>
     </option>
   </component>
-  <component name="RunManager" selected="Cargo Command.Run reference_counting">
+  <component name="RunManager" selected="Cargo Command.Run reference_cycles">
     <configuration name="&lt;template&gt;" type="TestNG" default="true" selected="false">
       <option name="MAIN_CLASS_NAME" />
       <option name="VM_PARAMETERS" value="-ea" />
@@ -237,6 +224,16 @@
       <envs />
       <method v="2" />
     </configuration>
+    <configuration name="Run reference_cycles" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
+      <option name="channel" value="DEFAULT" />
+      <option name="command" value="run --package reference_cycles --bin reference_cycles" />
+      <option name="allFeatures" value="false" />
+      <option name="nocapture" value="false" />
+      <option name="backtrace" value="SHORT" />
+      <option name="workingDirectory" value="file://$PROJECT_DIR$/reference_cycles" />
+      <envs />
+      <method v="2" />
+    </configuration>
     <configuration name="Run smart_pointers" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
       <option name="channel" value="DEFAULT" />
       <option name="command" value="run --package smart_pointers --bin smart_pointers" />
@@ -247,16 +244,6 @@
       <envs />
       <method v="2" />
     </configuration>
-    <configuration name="Test lib::tests (1)" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
-      <option name="channel" value="DEFAULT" />
-      <option name="command" value="test --package minigrep_v2 --lib tests" />
-      <option name="allFeatures" value="false" />
-      <option name="nocapture" value="false" />
-      <option name="backtrace" value="SHORT" />
-      <option name="workingDirectory" value="file://$PROJECT_DIR$/minigrep_v2" />
-      <envs />
-      <method v="2" />
-    </configuration>
     <configuration name="Test lib::tests" type="CargoCommandRunConfiguration" factoryName="Cargo Command" temporary="true">
       <option name="channel" value="DEFAULT" />
       <option name="command" value="test --package interior_mutability --lib tests" />
@@ -286,11 +273,11 @@
     </configuration>
     <recent_temporary>
       <list>
+        <item itemvalue="Cargo Command.Run reference_cycles" />
         <item itemvalue="Cargo Command.Run reference_counting" />
         <item itemvalue="Cargo Command.Test lib::tests" />
         <item itemvalue="Cargo Command.Test tests::it_sends_an_over_75_percent_warning_message" />
         <item itemvalue="Cargo Command.Run smart_pointers" />
-        <item itemvalue="Cargo Command.Test lib::tests (1)" />
       </list>
     </recent_temporary>
   </component>
@@ -330,8 +317,8 @@
     <frame x="1680" y="-410" width="1050" height="1657" extended-state="6" />
     <editor active="true" />
     <layout>
-      <window_info content_ui="combo" id="Project" order="0" sideWeight="0.49586776" visible="true" weight="0.26141885" />
+      <window_info content_ui="combo" id="Project" order="0" sideWeight="0.49644932" visible="true" weight="0.26141885" />
-      <window_info id="Structure" order="1" sideWeight="0.5041322" side_tool="true" visible="true" weight="0.26141885" />
+      <window_info id="Structure" order="1" sideWeight="0.50355065" side_tool="true" visible="true" weight="0.26141885" />
       <window_info id="Image Layers" order="2" />
       <window_info id="Designer" order="3" />
       <window_info id="Capture Tool" order="4" />
@@ -339,7 +326,7 @@
       <window_info id="Cargo" order="6" sideWeight="0.49791494" weight="0.3286119" />
       <window_info anchor="bottom" id="Message" order="0" />
       <window_info anchor="bottom" id="Find" order="1" weight="0.32979318" />
-      <window_info active="true" anchor="bottom" id="Run" order="2" visible="true" weight="0.29696578" />
+      <window_info anchor="bottom" id="Run" order="2" weight="0.29696578" />
       <window_info anchor="bottom" id="Debug" order="3" weight="0.4" />
       <window_info anchor="bottom" id="Cvs" order="4" weight="0.25" />
       <window_info anchor="bottom" id="Inspection" order="5" weight="0.4" />
@@ -749,9 +736,16 @@
         </state>
       </provider>
     </entry>
+    <entry file="file://$PROJECT_DIR$/reference_counting/src/main.rs">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="448">
+          <caret line="28" lean-forward="true" selection-start-line="28" selection-end-line="28" />
+        </state>
+      </provider>
+    </entry>
     <entry file="file://$PROJECT_DIR$/interior_mutability/src/lib.rs">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="672">
+        <state relative-caret-position="679">
           <caret line="55" column="69" selection-start-line="55" selection-start-column="69" selection-end-line="55" selection-end-column="69" />
           <folding>
             <element signature="e#1104#1105#0" expanded="true" />
@@ -760,10 +754,10 @@
         </state>
       </provider>
     </entry>
-    <entry file="file://$PROJECT_DIR$/reference_counting/src/main.rs">
+    <entry file="file://$PROJECT_DIR$/reference_cycles/src/main.rs">
       <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="320">
+        <state relative-caret-position="160">
-          <caret line="20" column="15" selection-start-line="20" selection-start-column="15" selection-end-line="20" selection-end-column="15" />
+          <caret line="10" column="11" lean-forward="true" selection-start-line="10" selection-start-column="11" selection-end-line="10" selection-end-column="11" />
         </state>
       </provider>
     </entry>

reference_cycles/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "reference_cycles"
+version = "0.1.0"
+authors = ["Timothy Warren <twarren@nabancard.com>"]
+edition = "2018"
+
+[dependencies]

reference_cycles/src/main.rs

@@ -0,0 +1,98 @@
+use std::rc::{Rc, Weak};
+use std::cell::RefCell;
+use List::{Cons, Nil};
+
+#[derive(Debug)]
+enum List {
+    Cons(i32, RefCell<Rc<List>>),
+    Nil,
+}
+
+impl List {
+    fn tail(&self) -> Option<&RefCell<Rc<List>>> {
+        match self {
+            Cons(_, item) => Some(item),
+            Nil => None,
+        }
+    }
+}
+
+fn cycle_example() {
+    let a = Rc::new(Cons(5, RefCell::new(Rc::new(Nil))));
+
+    println!("a initial rc count = {}", Rc::strong_count(&a));
+    println!("a next item = {:?}", a.tail());
+
+    let b = Rc::new(Cons(10, RefCell::new(Rc::clone(&a))));
+
+    println!("a rc count after b creation = {}", Rc::strong_count(&a));
+    println!("b initial rc count = {}", Rc::strong_count(&b));
+    println!("b next item = {:?}", b.tail());
+
+    if let Some(link) = a.tail() {
+        *link.borrow_mut() = Rc::clone(&b);
+    }
+
+    println!("b rc count after changing a = {}", Rc::strong_count(&b));
+    println!("a rc count after changing a = {}", Rc::strong_count(&a));
+
+    // Uncomment the next line to see that we have a cycle;
+    // it will overflow the stack
+    // println!("a next item = {:?}", a.tail());
+}
+
+#[derive(Debug)]
+struct Node {
+    value: i32,
+    parent: RefCell<Weak<Node>>,
+    children: RefCell<Vec<Rc<Node>>>,
+}
+
+fn weakref_example() {
+    let leaf = Rc::new(Node {
+        value: 3,
+        parent: RefCell::new(Weak::new()),
+        children: RefCell::new(vec![]),
+    });
+
+    println!(
+        "leaf strong = {}, weak = {}",
+        Rc::strong_count(&leaf),
+        Rc::weak_count(&leaf),
+    );
+
+    {
+        let branch = Rc::new(Node {
+            value: 5,
+            parent: RefCell::new(Weak::new()),
+            children: RefCell::new(vec![Rc::clone(&leaf)]),
+        });
+
+        *leaf.parent.borrow_mut() = Rc::downgrade(&branch);
+
+        println!(
+            "branch strong = {}, weak = {}",
+            Rc::strong_count(&branch),
+            Rc::weak_count(&branch),
+        );
+
+        println!(
+            "leaf strong = {}, weak = {}",
+            Rc::strong_count(&leaf),
+            Rc::weak_count(&leaf),
+        );
+    }
+
+    println!("leaf parent = {:?}", leaf.parent.borrow().upgrade());
+    println!(
+        "leaf strong = {}, weak = {}",
+        Rc::strong_count(&leaf),
+        Rc::weak_count(&leaf),
+    );
+}
+
+fn main() {
+    cycle_example();
+
+    weakref_example();
+}