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Return to Equivalent Effective Java Item 8, Effective C++, CPP, C++ Core Guidelines (CG) by Bjarne Stroustrup and Herb Sutter, Effective Java

In C++, resource management is crucial for writing robust, efficient, and maintainable code. The language provides several mechanisms for managing resources, including destructors, RAII (Resource Acquisition Is Initialization), and smart pointers. However, relying on finalizers (destructors that perform complex cleanup) and cleaners (external functions or methods invoked to clean up resources) can lead to several issues, such as undefined behavior, resource leaks, and poor performance. It's considered a best practice in C++ to avoid finalizers and cleaners in favor of more idiomatic and safer alternatives.

Avoiding finalizers and cleaners in C++ offers several key benefits:

1. **Deterministic Resource Management**: Relying on finalizers can lead to nondeterministic cleanup, making it harder to predict when resources will be released. RAII provides deterministic resource management, ensuring that resources are released as soon as they go out of scope. 2. **Simplified Code**: Finalizers and cleaners can complicate code by introducing additional methods or functions dedicated to cleanup, increasing the risk of errors. Using destructors and RAII simplifies resource management by bundling acquisition and cleanup within the same object. 3. **Performance Optimization**: Finalizers and cleaners can introduce unnecessary overhead, particularly if they involve complex logic or rely on garbage collection mechanisms. C++'s destructors and smart pointers are optimized for performance and minimize this overhead. 4. **Exception Safety**: Finalizers and cleaners may not be exception-safe, leading to resource leaks if an exception is thrown during cleanup. Destructors and RAII automatically handle exceptions, ensuring that resources are properly released even in the presence of exceptions.

RAII is a common pattern in C++ where resource acquisition and release are tied to the lifetime of an object. This ensures that resources are automatically cleaned up when the object goes out of scope, avoiding the need for finalizers.

1. Finalizer Approach (Anti-Pattern)

```cpp class Resource { public:

   Resource() {
       // Acquire resource
   }

   ~Resource() {
       // Clean up resource
       if (cleanUpRequired) {
           cleanUp();
       }
   }

private:

   void cleanUp() {
       // Complex cleanup logic
   }

   bool cleanUpRequired = true;

In this example, the destructor acts as a finalizer, performing complex cleanup logic that is conditional and may introduce errors or undefined behavior.

1. RAII Approach

```cpp class Resource { public:

   Resource() {
       // Acquire resource
   }

   ~Resource() {
       // Clean up resource
   }

   // RAII: No need for complex finalizers or conditionals

void useResource() {

   Resource resource; // Automatically cleaned up when it goes out of scope
   // Use the resource

In this improved version, the resource is acquired in the constructor and released in the destructor, following the RAII pattern. The cleanup is deterministic and simple, with no need for complex finalizers.

Smart pointers in C++ automatically manage the lifetime of dynamically allocated objects, ensuring that memory is released when the pointer goes out of scope. This avoids the need for manual cleaners.

1. Cleaner Approach (Anti-Pattern)

```cpp class Resource { public:

   Resource() {
       // Allocate memory
       data = new int[100];
   }

   ~Resource() {
       // Manually clean up memory
       if (data) {
           delete[] data;
       }
   }

private:

   int* data;

void useResource() {

   Resource resource;
   // Use the resource

In this example, the destructor acts as a cleaner by manually deallocating memory, which can lead to memory leaks if not handled correctly.

1. Smart Pointer Approach

```cpp

1. include <memory>

class Resource { public:

   Resource() : data(std::make_unique(100)) {
       // Memory is automatically managed by the smart pointer
   }

private:

   std::unique_ptr data;

void useResource() {

   Resource resource; // Memory is automatically cleaned up when it goes out of scope
   // Use the resource

In this improved version, `std::unique_ptr` is used to manage the memory, eliminating the need for manual cleanup. The smart pointer ensures that the memory is automatically deallocated when the `Resource` object is destroyed.

In cases where you need shared ownership of resources or custom cleanup logic, `std::shared_ptr` with a custom deleter can be used instead of finalizers or cleaners.

1. Finalizer and Cleaner Approach (Anti-Pattern)

```cpp class Resource { public:

   Resource() {
       // Allocate and initialize resource
   }

   ~Resource() {
       // Finalize and clean up resource
       if (initialized) {
           finalize();
       }
   }

private:

   void finalize() {
       // Custom cleanup logic
   }

   bool initialized = true;

void useResource() {

   Resource* resource = new Resource();
   // Use the resource
   delete resource; // Manual deletion with custom finalizer

In this example, the destructor includes a custom finalizer for resource cleanup, which adds complexity and potential for errors.

1. `std::shared_ptr` with Custom Deleter

```cpp

1. include <memory>

void customDeleter(Resource* resource) {

   // Custom cleanup logic
   delete resource;

void useResource() {

   std::shared_ptr resource(new Resource(), customDeleter);
   // Use the resource
   // Resource is automatically cleaned up with custom deleter when the shared_ptr goes out of scope

In this improved version, `std::shared_ptr` with a custom deleter is used to manage the resource. The custom deleter ensures that any necessary cleanup logic is executed when the `Resource` object is no longer needed, without relying on complex finalizers or cleaners.

Avoid finalizers and cleaners in the following scenarios:

- **Memory Management**: Use RAII and smart pointers (`std::unique_ptr`, `std::shared_ptr`) to automatically manage memory and other resources, ensuring deterministic cleanup. - **Complex Resource Cleanup**: When resources require complex cleanup, prefer using custom deleters with smart pointers rather than embedding cleanup logic in destructors. - **Exception Safety**: Rely on destructors and RAII to ensure resources are released even in the presence of exceptions, avoiding the pitfalls of manual cleanup in finalizers or cleaners.

In C++, avoiding finalizers and cleaners in favor of RAII, smart pointers, and custom deleters is a best practice that leads to more robust, maintainable, and efficient code. By leveraging these idiomatic C++ mechanisms, you can ensure that resources are managed deterministically, exceptions are handled safely, and your code remains clean and simple. This approach aligns with modern C++ best practices and helps you avoid common pitfalls associated with manual resource management.

For more information on best practices in C++ and resource management techniques, consider exploring the following resources:

• https://en.cppreference.com/w/cpp/language/raii
• https://en.cppreference.com/w/cpp/memory/unique_ptr
• https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines

These resources provide additional insights and best practices for writing efficient and optimized code in C++.

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