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Item 6: CPP Best Practices - Avoid creating unnecessary objects
Introduction to Avoiding Unnecessary Object Creation in [[CPP]]
Why Avoid Unnecessary Object Creation?
Example 1: Reuse Existing Objects Instead of Creating New Ones
Example 2: Use Initialization Lists in Constructors
Example 3: Use Move Semantics Instead of Copying
Example 4: Avoid Unnecessary Dynamic Memory Allocation
Example 5: Use `emplace` Instead of `push_back` When Inserting into Containers
When to Avoid Unnecessary Object Creation in [[C++]]
Conclusion
Further Reading and References
Fair Use Sources

Item 6: CPP Best Practices - Avoid creating unnecessary objects

Return to Equivalent Effective Java Item 6, Effective C++, CPP, C++ Core Guidelines (CG) by Bjarne Stroustrup and Herb Sutter, Effective Java

Introduction to Avoiding Unnecessary Object Creation in [[CPP]]

In C++, object creation is a fundamental aspect of programming. However, creating unnecessary objects can lead to performance issues such as increased memory usage, higher overhead in constructors and destructors, and reduced application efficiency. By avoiding unnecessary object creation, you can write more efficient and optimized code, leading to better performance and resource utilization in your C++ applications.

Why Avoid Unnecessary Object Creation?

Creating objects in C++ incurs a cost because: 1. **Memory Usage**: Each object consumes memory, and unnecessary objects can lead to higher memory consumption, potentially causing memory exhaustion in resource-constrained environments. 2. **Constructor and Destructor Overhead**: Every object creation involves calling a constructor, and every destruction involves calling a destructor. Unnecessary objects increase the overhead associated with these operations, reducing performance. 3. **Performance Impact**: Constant creation and destruction of objects can slow down your application, especially in performance-critical sections of the code.

Example 1: Reuse Existing Objects Instead of Creating New Ones

Unnecessary Object Creation

```cpp std::string concatenate(const std::string& str1, const std::string& str2) {

   return std::string(str1 + str2);  // Unnecessary creation of a new std::string object

} ```

Avoiding Unnecessary Object Creation

```cpp std::string concatenate(const std::string& str1, const std::string& str2) {

   return str1 + str2;  // Reuse the existing std::string object without creating a new one

} ```

In this example, the unnecessary creation of a new `std::string` object is avoided by directly returning the concatenated string. C++'s string handling can efficiently reuse existing objects.

Example 2: Use Initialization Lists in Constructors

Initialization lists are an efficient way to initialize class members without creating unnecessary temporary objects.

Unnecessary Object Creation

```cpp class Rectangle {

   int width, height;

public:

   Rectangle(int w, int h) {
       width = w;  // Assignment after default initialization
       height = h; // Assignment after default initialization
   }

}; ```

Avoiding Unnecessary Object Creation

```cpp class Rectangle {

   int width, height;

public:

   Rectangle(int w, int h) : width(w), height(h) {}  // Use initialization list to avoid unnecessary default initialization

}; ```

In this example, using an initialization list avoids unnecessary object creation by directly initializing member variables without an intermediate default construction.

Example 3: Use Move Semantics Instead of Copying

In C++11 and later, move semantics allow you to transfer ownership of resources, avoiding unnecessary object copying.

Unnecessary Object Creation Through Copying

```cpp std::vector<int> createLargeVector() {

   std::vector vec(1000000, 1);
   return vec;  // Copying the large vector

} ```

Avoiding Unnecessary Object Creation with Move Semantics

```cpp std::vector<int> createLargeVector() {

   std::vector vec(1000000, 1);
   return std::move(vec);  // Move the large vector instead of copying it

} ```

In this example, using `std::move` avoids the unnecessary creation of a copied `std::vector`, improving performance by transferring ownership of the existing object.

Example 4: Avoid Unnecessary Dynamic Memory Allocation

Dynamic memory allocation (using `new` and `delete`) can lead to unnecessary object creation, particularly when it is avoidable.

Unnecessary Object Creation with Dynamic Allocation

```cpp int* createArray(int size) {

   return new int[size];  // Dynamic allocation of an array

} ```

Avoiding Unnecessary Object Creation with Automatic Storage

```cpp std::vector<int> createArray(int size) {

   return std::vector(size);  // Use automatic storage and RAII with std::vector

} ```

In this example, using `std::vector` instead of manually managing dynamic memory with `new` and `delete` avoids unnecessary object creation and leverages C++'s RAII (Resource Acquisition Is Initialization) principle.

Example 5: Use `emplace` Instead of `push_back` When Inserting into Containers

Using `emplace` allows you to construct objects in place within a container, avoiding unnecessary temporary object creation.

Unnecessary Object Creation with `push_back`

```cpp std::vector<std::pair<int, std::string» vec; vec.push_back(std::make_pair(1, “one”)); // Creates a temporary pair object ```

Avoiding Unnecessary Object Creation with `emplace`

```cpp std::vector<std::pair<int, std::string» vec; vec.emplace_back(1, “one”); // Constructs the pair directly in place ```

In this example, using `emplace_back` avoids the unnecessary creation of a temporary `std::pair` object by constructing it directly in the container.

When to Avoid Unnecessary Object Creation in [[C++]]

Avoiding unnecessary object creation is particularly important in the following scenarios: - **Performance-Critical Applications**: In applications where performance is crucial, minimizing object creation can lead to significant improvements in speed and responsiveness. - **Memory-Constrained Environments**: In environments with limited memory, avoiding unnecessary objects can prevent out-of-memory errors and reduce the overhead associated with dynamic memory allocation and garbage collection. - **Embedded Systems**: In embedded systems, where resources are limited, minimizing unnecessary object creation is essential for maintaining efficiency and stability.

Conclusion

In C++, avoiding unnecessary object creation is a best practice that leads to more efficient, optimized, and maintainable code. By reusing existing objects, using initialization lists, leveraging move semantics, avoiding unnecessary dynamic memory allocation, and using `emplace` for container insertion, you can reduce memory consumption and improve the performance of your applications. This approach aligns well with modern C++ development practices, where efficiency and resource management are key considerations.