__get and __set for property access in PHP - Time & Space Complexity

Time Complexity: __get and __set for property access

O(1)

Understanding Time Complexity

When using __get and __set in PHP, it's important to understand how accessing or setting properties affects performance.

We want to know how the time to access or set a property changes as the number of properties or operations grows.

Scenario Under Consideration

Analyze the time complexity of the following PHP code using __get and __set.

class Example {
    private array $data = [];

    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }

    public function __get(string $name): mixed {
        return $this->data[$name] ?? null;
    }
}

$obj = new Example();
$obj->foo = 'bar';
echo $obj->foo;
    

This code stores properties in an internal array and accesses them via magic methods.

Identify Repeating Operations

Look at what repeats when we access or set properties.

• Primary operation: Array key assignment and lookup inside __set and __get.
• How many times: Each property access or set triggers one array operation.

How Execution Grows With Input

As the number of properties stored grows, each access or set still does one array operation.

Input Size (n)	Approx. Operations per Access/Set
10	1
100	1
1000	1

Pattern observation: Each property access or set takes about the same time, no matter how many properties exist.

Final Time Complexity

Time Complexity: O(1)

This means accessing or setting a property using __get or __set takes a constant amount of time regardless of how many properties are stored.

Common Mistake

[X] Wrong: "Accessing properties with __get and __set gets slower as more properties are added."

[OK] Correct: The internal array uses fast key lookup, so each access or set is quick and does not slow down with more properties.

Interview Connect

Understanding how magic methods like __get and __set work helps you explain object behavior clearly and shows you know how PHP handles property access efficiently.

Self-Check

What if we changed the internal storage from an array to a linked list? How would the time complexity of property access change?

Practice

1.

What is the main purpose of the __get magic method in PHP?

easy

A. To control reading of inaccessible or undefined properties

B. To delete object properties

C. To initialize object properties automatically

D. To overload methods dynamically

Solution

1. Step 1: Understand the role of __get

   The __get method is called when reading a property that is inaccessible or not defined in the object.

2. Step 2: Compare with other options

   Options B, C, and D describe different behaviors unrelated to __get. Only To control reading of inaccessible or undefined properties correctly describes its purpose.

3. Final Answer:

   To control reading of inaccessible or undefined properties -> Option A

4. Quick Check:

   __get reads missing properties = A [OK]

Hint: Remember __get triggers on reading missing properties [OK]

Common Mistakes:

• Confusing __get with __set
• Thinking __get initializes properties
• Assuming __get deletes properties

2.

Which of the following is the correct syntax to define the __set magic method in a PHP class?

class Example {
    ?
}

easy

A. public function __set($name, $value) { /* code */ }

B. public function __set($value, $name) { /* code */ }

C. public function __set() { /* code */ }

D. public function set($name, $value) { /* code */ }

Solution

1. Step 1: Recall __set method signature

   The __set method must accept two parameters: the property name and the value to assign.

2. Step 2: Check parameter order and method name

   public function __set($name, $value) { /* code */ } correctly uses __set($name, $value). public function __set($value, $name) { /* code */ } reverses parameters, C has no parameters, and D uses wrong method name.

3. Final Answer:

   public function __set($name, $value) { /* code */ } -> Option A

4. Quick Check:

   __set($name, $value) correct signature = B [OK]

Hint: __set always takes property name first, then value [OK]

Common Mistakes:

• Swapping parameter order
• Omitting parameters
• Using wrong method name without double underscore

3.

What will be the output of the following PHP code?

class Test {
    private $data = [];
    public function __set($name, $value) {
        $this->data[$name] = $value;
    }
    public function __get($name) {
        return $this->data[$name] ?? 'Not found';
    }
}

$obj = new Test();
$obj->color = 'red';
echo $obj->color . ' ' . $obj->size;

medium

A. red null

B. red Not found

C. Notice error and red

D. red

Solution

1. Step 1: Understand property setting

   Setting $obj->color = 'red' calls __set, storing 'red' in $data['color'].

2. Step 2: Understand property getting

   Accessing $obj->color returns 'red'. Accessing $obj->size returns 'Not found' because $data['size'] is not set.

3. Final Answer:

   red Not found -> Option B

4. Quick Check:

   Defined property returns value, undefined returns 'Not found' = D [OK]

Hint: Undefined property returns default from __get using ?? operator [OK]

Common Mistakes:

• Expecting undefined property to be empty string
• Ignoring null coalescing operator
• Assuming Notice error on missing array key

4.

Consider this PHP class:

class Sample {
    private $props = [];
    public function __set($name, $value) {
        $this->props[$name] = $value;
    }
    public function __get($name) {
        return $this->props[$name];
    }
}

$obj = new Sample();
echo $obj->missing;

What error will occur and how to fix it?

medium

A. No error; outputs empty string

B. Fatal error; fix by declaring property publicly

C. Parse error; fix by adding return type

D. Undefined index notice; fix by using null coalescing in __get

Solution

1. Step 1: Identify error cause

   Accessing $obj->missing calls __get, which returns $this->props['missing']. Since 'missing' key is not set, PHP raises an undefined index notice.

2. Step 2: Fix the error

   Modify __get to return $this->props[$name] ?? null or a default value to avoid notice.

3. Final Answer:

   Undefined index notice; fix by using null coalescing in __get -> Option D

4. Quick Check:

   Missing key causes notice; use ?? to fix = C [OK]

Hint: Use ?? operator in __get to avoid undefined index notices [OK]

Common Mistakes:

• Ignoring undefined index notices
• Trying to declare missing properties publicly
• Confusing parse errors with runtime notices

5.

You want to create a PHP class that stores any property set dynamically and logs every property read or write. Which implementation correctly uses __get and __set to achieve this?

class Logger {
    private $data = [];
    public function __set($name, $value) {
        // ???
    }
    public function __get($name) {
        // ???
    }
}

hard

A. In __set: echo write log only; in __get: return value without logging

B. In __set: only store value; in __get: return value without logging

C. In __set: store value and echo write log; in __get: echo read log and return value or null

D. In __set: store value and return it; in __get: echo read log only

Solution

1. Step 1: Understand logging requirements

   We must log both property writes and reads, and store values dynamically.

2. Step 2: Check each option's behavior

   In __set: store value and echo write log; in __get: echo read log and return value or null stores the value in $data and echoes a write log in __set, and echoes a read log and returns the stored value or null in __get. This meets all requirements.

3. Final Answer:

   In __set: store value and echo write log; in __get: echo read log and return value or null -> Option C

4. Quick Check:

   Store and log on read/write = A [OK]

Hint: Log inside both __get and __set while storing values [OK]

Common Mistakes:

• Logging only on write or only on read
• Not returning value in __get
• Returning value in __set (which should be void)