Manual includes vs autoloading in PHP - Performance Comparison

Time Complexity: Manual includes vs autoloading

O(n)

Understanding Time Complexity

When loading PHP classes, we can do it manually or automatically. Understanding how this affects performance helps us write faster programs.

We want to know how the time to load classes grows as the number of classes increases.

Scenario Under Consideration

Analyze the time complexity of manually including files versus using autoloading.

// Manual includes
include 'ClassA.php';
include 'ClassB.php';
include 'ClassC.php';
// ... repeated for each class

// Autoloading example
spl_autoload_register(function ($class) {
    include $class . '.php';
});

// When a class is used, PHP loads it automatically
$obj = new ClassA();

This code shows two ways to load classes: manually listing each file or letting PHP load them when needed.

Identify Repeating Operations

Look at what repeats as the number of classes grows.

• Primary operation: Including class files from disk.
• How many times: Manual includes run once per class upfront; autoloading includes only when a class is used.

How Execution Grows With Input

As the number of classes (n) grows, manual includes load all files every time, while autoloading loads only needed files.

Input Size (n)	Approx. Operations (file loads)
10	Manual: 10 includes; Autoload: up to 10 includes as needed
100	Manual: 100 includes; Autoload: only includes used classes
1000	Manual: 1000 includes; Autoload: only includes used classes

Pattern observation: Manual includes always load all files, so work grows directly with total classes. Autoloading loads files only when needed, so work depends on usage, not total classes.

Final Time Complexity

Time Complexity: O(n)

This means manual includes take time proportional to the total number of classes, while autoloading only loads what is needed, saving time when many classes exist but few are used.

Common Mistake

[X] Wrong: "Manual includes and autoloading always take the same time because all classes must be loaded eventually."

[OK] Correct: Autoloading loads classes only when used, so if many classes exist but only a few are needed, it saves time compared to loading all files upfront.

Interview Connect

Understanding how loading classes affects performance shows you think about efficient code. This skill helps you write programs that run faster and use resources wisely.

Self-Check

"What if autoloading used a complex search through many directories before loading a class? How would that affect time complexity?"