Type hinting with parent classes in PHP - Time & Space Complexity

Time Complexity: Type hinting with parent classes

O(n)

Understanding Time Complexity

We want to understand how the time it takes to run code changes when using type hints with parent classes in PHP.

Specifically, how does checking types against parent classes affect the speed as input grows?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Animal {}
class Dog extends Animal {}

function feedAnimal(Animal $animal) {
    // feeding logic here
}

$dogs = array_fill(0, $n, new Dog());
foreach ($dogs as $dog) {
    feedAnimal($dog);
}
    

This code creates an array of Dog objects and feeds each one using a function that requires an Animal type hint.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through the array of Dog objects.
• How many times: Exactly once for each Dog in the array, so n times.

How Execution Grows With Input

As the number of Dog objects increases, the feeding function is called once per object.

Input Size (n)	Approx. Operations
10	10 calls to feedAnimal()
100	100 calls to feedAnimal()
1000	1000 calls to feedAnimal()

Pattern observation: The number of operations grows directly with the number of objects.

Final Time Complexity

Time Complexity: O(n)

This means the time to run the code grows in a straight line as the number of objects increases.

Common Mistake

[X] Wrong: "Type hinting with parent classes slows down the code exponentially because it checks all subclasses."

[OK] Correct: PHP only checks the type once per call, and it does not repeatedly check all subclasses. The time grows linearly with the number of calls, not exponentially.

Interview Connect

Understanding how type hinting affects performance helps you write clear and efficient code, a skill valued in real projects and interviews.

Self-Check

"What if we changed the array to hold different subclasses of Animal instead of just Dog? How would the time complexity change?"