Add Rust and C++ linked list implementations with build/debug configs

Rust version in src/main.rs (Cargo project) and a C++ port in cpp/main.cpp
using raw pointers, both with VS Code build tasks and gdb-based debug
configs. Vendors vscode-debug-visualizer and visualization as submodules
for reference while building a custom node-table graph visualizer.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

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+/target
+/cpp/list_example_cpp

.gitmodules

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+[submodule "external/vscode-debug-visualizer"]
+	path = external/vscode-debug-visualizer
+	url = https://github.com/hediet/vscode-debug-visualizer.git
+[submodule "external/visualization"]
+	path = external/visualization
+	url = https://github.com/hediet/visualization.git

.vscode/launch.json

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+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Debug list_example (Rust)",
+            "type": "cppdbg",
+            "request": "launch",
+            "program": "${workspaceFolder}/target/debug/list_example",
+            "args": [],
+            "stopAtEntry": false,
+            "cwd": "${workspaceFolder}",
+            "environment": [],
+            "externalConsole": false,
+            "MIMode": "gdb",
+            "miDebuggerPath": "/usr/bin/rust-gdb",
+            "preLaunchTask": "cargo build",
+            "setupCommands": [
+                {
+                    "description": "Enable pretty-printing for gdb",
+                    "text": "-enable-pretty-printing",
+                    "ignoreFailures": true
+                }
+            ]
+        },
+        {
+            "name": "Debug list_example (C++)",
+            "type": "cppdbg",
+            "request": "launch",
+            "program": "${workspaceFolder}/cpp/list_example_cpp",
+            "args": [],
+            "stopAtEntry": false,
+            "cwd": "${workspaceFolder}/cpp",
+            "environment": [],
+            "externalConsole": false,
+            "MIMode": "gdb",
+            "miDebuggerPath": "/usr/bin/gdb",
+            "preLaunchTask": "g++ build cpp/main.cpp",
+            "setupCommands": [
+                {
+                    "description": "Enable pretty-printing for gdb",
+                    "text": "-enable-pretty-printing",
+                    "ignoreFailures": true
+                },
+                {
+                    "description": "Don't truncate long arrays (needed for Debug Visualizer JSON)",
+                    "text": "-gdb-set print elements 0",
+                    "ignoreFailures": true
+                },
+                {
+                    "description": "Don't truncate long strings (needed for Debug Visualizer JSON)",
+                    "text": "-gdb-set print characters 0",
+                    "ignoreFailures": true
+                }
+            ]
+        }
+    ]
+}

.vscode/tasks.json

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+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "cargo build",
+            "type": "shell",
+            "command": "cargo",
+            "args": ["build"],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "problemMatcher": ["$rustc"]
+        },
+        {
+            "label": "g++ build cpp/main.cpp",
+            "type": "cppbuild",
+            "command": "/usr/bin/g++",
+            "args": [
+                "-std=c++17",
+                "-g",
+                "-Wall",
+                "-Wextra",
+                "${workspaceFolder}/cpp/main.cpp",
+                "-o",
+                "${workspaceFolder}/cpp/list_example_cpp"
+            ],
+            "options": {
+                "cwd": "${workspaceFolder}/cpp"
+            },
+            "group": "build",
+            "problemMatcher": ["$gcc"]
+        }
+    ]
+}

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "list_example"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "list_example"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

cpp/main.cpp

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+#include <iostream>
+#include <optional>
+#include <sstream>
+
+// A single node containing data and a raw pointer to the next node
+template <typename T>
+struct Node {
+    T data;
+    Node<T>* next;
+};
+
+// The main wrapper for the linked list tracking the head node
+template <typename T>
+class LinkedList {
+public:
+    LinkedList() : head_(nullptr) {}
+
+    ~LinkedList() {
+        Node<T>* current = head_;
+        while (current) {
+            Node<T>* next = current->next;
+            delete current;
+            current = next;
+        }
+    }
+
+    // Raw-pointer ownership can't be safely duplicated by a shallow copy
+    LinkedList(const LinkedList&) = delete;
+    LinkedList& operator=(const LinkedList&) = delete;
+
+    // Add a new element to the front of the list
+    void push_front(T data) {
+        head_ = new Node<T>{std::move(data), head_};
+    }
+
+    // Remove and return the front element of the list
+    std::optional<T> pop_front() {
+        if (!head_) {
+            return std::nullopt;
+        }
+        Node<T>* old_head = head_;
+        T data = std::move(old_head->data);
+        head_ = old_head->next;
+        delete old_head;
+        return data;
+    }
+
+    // Read the front element without removing it
+    const T* peek_front() const {
+        return head_ ? &head_->data : nullptr;
+    }
+
+    // Build a JSON string describing the list as a graph, for the VS Code
+    // "Debug Visualizer" extension: watch `list.toDebugGraph()` while paused.
+    // Schema: https://hediet.github.io/visualization/docs/visualization-data-schema.json
+    std::string toDebugGraph() const {
+        std::ostringstream json;
+        json << "{\"kind\":{\"graph\":true},\"nodes\":[";
+        for (Node<T>* n = head_; n; n = n->next) {
+            if (n != head_) json << ",";
+            json << "{\"id\":\"" << n << "\",\"label\":\"" << n->data << "\"}";
+        }
+        json << "],\"edges\":[";
+        for (Node<T>* n = head_; n && n->next; n = n->next) {
+            if (n != head_) json << ",";
+            json << "{\"from\":\"" << n << "\",\"to\":\"" << n->next << "\"}";
+        }
+        json << "]}";
+        return json.str();
+    }
+
+private:
+    Node<T>* head_;
+};
+
+// Force instantiation of every member, including toDebugGraph(), which
+// nothing in this file calls directly -- without this, gdb has no symbol
+// to invoke from the debugger's watch expression.
+template class LinkedList<int>;
+
+int main() {
+    LinkedList<int> list;
+
+    // Demonstrate pushing items
+    list.push_front(10);
+    list.push_front(20);
+    list.push_front(30);
+
+    // Demonstrate peeking at the top item
+    if (const int* top = list.peek_front()) {
+        std::cout << "Top element: " << *top << "\n"; // Output: 30
+    }
+
+    // Demonstrate popping items
+    while (auto value = list.pop_front()) {
+        std::cout << "Popped: " << *value << "\n";
+    }
+
+    return 0;
+}

src/main.rs

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+// A single node containing data and an optional pointer to the next node
+struct Node<T> {
+    data: T,
+    next: Option<Box<Node<T>>>,
+}
+
+// The main wrapper for the linked list tracking the head node
+pub struct LinkedList<T> {
+    head: Option<Box<Node<T>>>,
+}
+
+impl<T> LinkedList<T> {
+    // Create an empty linked list
+    pub fn new() -> Self {
+        LinkedList { head: None }
+    }
+
+    // Add a new element to the front of the list
+    pub fn push_front(&mut self, data: T) {
+        let new_node = Box::new(Node {
+            data,
+            // .take() temporarily leaves None in self.head and extracts the value
+            next: self.head.take(), 
+        });
+        self.head = Some(new_node);
+    }
+
+    // Remove and return the front element of the list
+    pub fn pop_front(&mut self) -> Option<T> {
+        self.head.take().map(|node| {
+            self.head = node.next;
+            node.data
+        })
+    }
+
+    // Read the front element without removing it
+    pub fn peek_front(&self) -> Option<&T> {
+        self.head.as_ref().map(|node| &node.data)
+    }
+}
+
+fn main() {
+    let mut list = LinkedList::new();
+
+    // Demonstrate pushing items
+    list.push_front(10);
+    list.push_front(20);
+    list.push_front(30);
+
+    // Demonstrate peaking at the top item
+    println!("Top element: {:?}", list.peek_front()); // Output: Some(30)
+
+    // Demonstrate popping items
+    while let Some(value) = list.pop_front() {
+        println!("Popped: {}", value);
+    }
+}