Refactor Menu constructors to use delegation pattern

Updated the Menu class on macOS to use delegating constructors, consolidating initialization logic into the parameterized constructor. This eliminates code duplication and ensures consistent setup whether creating a new NSMenu or wrapping an existing native menu object. Also updated documentation to illustrate the constructor delegation pattern.

Author: lijy91

.cursor/rules/pimpl-pattern.mdc

@@ -233,6 +233,82 @@ MyClass::MyClass() : pimpl_(std::make_unique<Impl>()) {}
 MyClass::~MyClass() = default;  // unique_ptr handles cleanup
 ```
 
+#### Constructor Delegation Pattern
+
+When a class has multiple constructors, use **delegating constructors** to avoid code duplication. The default constructor delegates to the parameterized constructor:
+
+```cpp
+// Header
+class TrayIcon {
+public:
+    TrayIcon();                  // Default constructor
+    TrayIcon(void* native_tray); // Wraps existing native object
+    virtual ~TrayIcon();
+
+private:
+    class Impl;
+    std::unique_ptr<Impl> pimpl_;
+};
+
+// Implementation - delegate to avoid duplication
+TrayIcon::TrayIcon() : TrayIcon(nullptr) {}  // Delegate to parameterized constructor
+
+TrayIcon::TrayIcon(void* tray) {
+    // Handle both cases in one place
+    NSStatusItem* status_item = nullptr;
+    
+    if (tray == nullptr) {
+        // Create new platform object
+        NSStatusBar* status_bar = [NSStatusBar systemStatusBar];
+        status_item = [status_bar statusItemWithLength:NSVariableStatusItemLength];
+    } else {
+        // Wrap existing platform object
+        status_item = (__bridge NSStatusItem*)tray;
+    }
+    
+    // All initialization logic in one place
+    pimpl_ = std::make_unique<Impl>(status_item);
+    
+    // Additional setup that applies to both cases
+    if (pimpl_->status_item_) {
+        // Configure the status item...
+    }
+}
+
+TrayIcon::~TrayIcon() = default;
+```
+
+**Benefits:**
+- ✅ Eliminates duplicate initialization code
+- ✅ Single source of truth for object setup
+- ✅ Easier to maintain and update
+- ✅ Prevents inconsistencies between constructors
+
+**Without Delegation (Don't do this):**
+```cpp
+// Bad - duplicated initialization logic
+TrayIcon::TrayIcon() : pimpl_(std::make_unique<Impl>()) {
+    NSStatusBar* status_bar = [NSStatusBar systemStatusBar];
+    NSStatusItem* status_item = [status_bar statusItemWithLength:NSVariableStatusItemLength];
+    pimpl_->status_item_ = status_item;
+    
+    // Setup code duplicated...
+    if (pimpl_->status_item_) {
+        // Configure...
+    }
+}
+
+TrayIcon::TrayIcon(void* tray) : pimpl_(std::make_unique<Impl>()) {
+    NSStatusItem* status_item = (__bridge NSStatusItem*)tray;
+    pimpl_->status_item_ = status_item;
+    
+    // Same setup code duplicated again!
+    if (pimpl_->status_item_) {
+        // Configure...
+    }
+}
+```
+
 ### 4. Manager Classes with PIMPL
 
 Singleton managers also use PIMPL ([window_manager.h](mdc:src/window_manager.h)):

src/platform/macos/menu_macos.mm

@@ -589,34 +589,21 @@ - (void)menuDidClose:(NSMenu*)menu {
 };
 
 // Menu implementation
-Menu::Menu() : id(IdAllocator::Allocate<Menu>()) {
-  NSMenu* ns_menu = [[NSMenu alloc] init];
-  pimpl_ = std::make_unique<Impl>(ns_menu);
-  objc_setAssociatedObject(ns_menu, kMenuIdKey, [NSNumber numberWithUnsignedInt:id],
-                           OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+Menu::Menu() : Menu(nullptr) {}
 
-  // 设置默认的 Block 处理器，直接发送事件
-  pimpl_->delegate_.openedBlock = ^(MenuId menu_id) {
-    try {
-      Emit<MenuOpenedEvent>(menu_id);
-    } catch (...) {
-      // Protect against event emission exceptions
-    }
-  };
+Menu::Menu(void* native_menu) : id(IdAllocator::Allocate<Menu>()) {
+  NSMenu* ns_menu = nullptr;
 
-  pimpl_->delegate_.closedBlock = ^(MenuId menu_id) {
-    try {
-      Emit<MenuClosedEvent>(menu_id);
-    } catch (...) {
-      // Protect against event emission exceptions
-    }
-  };
-}
+  if (native_menu == nullptr) {
+    // Create new platform object
+    ns_menu = [[NSMenu alloc] init];
+  } else {
+    // Wrap existing platform object
+    ns_menu = (__bridge NSMenu*)native_menu;
+  }
 
-Menu::Menu(void* native_menu)
-    : id(IdAllocator::Allocate<Menu>()),
-      pimpl_(std::make_unique<Impl>((__bridge NSMenu*)native_menu)) {
-  NSMenu* ns_menu = (__bridge NSMenu*)native_menu;
+  // All initialization logic in one place
+  pimpl_ = std::make_unique<Impl>(ns_menu);
   objc_setAssociatedObject(ns_menu, kMenuIdKey, [NSNumber numberWithUnsignedInt:id],
                            OBJC_ASSOCIATION_RETAIN_NONATOMIC);