get, set, isset, unset

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 46 of 91.

PHP provides four magic methods that intercept property access: __get(), __set(), __isset(), and __unset(). These are triggered when you try to access properties that don't exist or are inaccessible.

The __get() method is called when reading an inaccessible property, while __set() handles writing to one. This lets you create dynamic properties or add logic when properties are accessed:

<?php
class DynamicObject {
    private array $data = [];
    
    public function __get(string $name): mixed {
        return $this->data[$name] ?? null;
    }
    
    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }
}

$obj = new DynamicObject();
$obj->title = "Hello";
$obj->count = 42;
echo $obj->title . " - " . $obj->count;

Output:

Hello - 42

The __isset() method is triggered by isset() or empty(), and __unset() responds to the unset() function:

<?php
class DynamicObject {
    private array $data = [];
    
    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }
    
    public function __isset(string $name): bool {
        return isset($this->data[$name]);
    }
    
    public function __unset(string $name): void {
        unset($this->data[$name]);
    }
}

$obj = new DynamicObject();
$obj->name = "Test";
echo isset($obj->name) ? "exists" : "missing";

Output:

exists

These methods are commonly used to create flexible data containers, implement lazy loading, or build objects that behave like arrays while maintaining object-oriented structure.

Challenge

Easy

Let's build a flexible configuration manager that stores settings dynamically using magic methods. Your class will intercept property access to manage configuration values, check if settings exist, and remove them when needed — all without explicitly defining each property.

You'll organize your code across two files:

Config.php — Create a Config class that uses a private array to store configuration values internally. Implement all four property magic methods:
- __get($name) — Returns the value for the given key, or "undefined" if the key doesn't exist
- __set($name, $value) — Stores the value under the given key
- __isset($name) — Returns whether the key exists in the configuration
- __unset($name) — Removes the key from the configuration
Also add a method count() that returns the number of stored settings.
main.php — Include the Config file. You'll receive three inputs: a setting name, a setting value, and a second setting name. Create a Config instance and perform these operations:
- Set the first setting to the given value
- Print whether the first setting exists using isset() — output "exists" or "missing"
- Print the value of the first setting
- Print the current count of settings
- Use unset() to remove the first setting
- Print whether the first setting exists now — output "exists" or "missing"
- Print the value of the second setting (which was never set)

Each output should be on its own line. The magic methods let you interact with your Config object using natural property syntax like $config->theme = "dark" and isset($config->theme), even though no actual properties are defined.

Cheat sheet

PHP provides four magic methods to intercept property access:

__get(string $name): mixed — Called when reading an inaccessible property
__set(string $name, mixed $value): void — Called when writing to an inaccessible property
__isset(string $name): bool — Triggered by isset() or empty()
__unset(string $name): void — Triggered by unset()

Example of __get() and __set():

<?php
class DynamicObject {
    private array $data = [];
    
    public function __get(string $name): mixed {
        return $this->data[$name] ?? null;
    }
    
    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }
}

$obj = new DynamicObject();
$obj->title = "Hello";
echo $obj->title; // Hello

Example of __isset() and __unset():

<?php
class DynamicObject {
    private array $data = [];
    
    public function __set(string $name, mixed $value): void {
        $this->data[$name] = $value;
    }
    
    public function __isset(string $name): bool {
        return isset($this->data[$name]);
    }
    
    public function __unset(string $name): void {
        unset($this->data[$name]);
    }
}

$obj = new DynamicObject();
$obj->name = "Test";
echo isset($obj->name) ? "exists" : "missing"; // exists

These methods enable dynamic properties, lazy loading, and flexible data containers while maintaining object-oriented structure.

Try it yourself

<?php

require_once 'Config.php';

// Read inputs
$settingName1 = trim(fgets(STDIN));
$settingValue = trim(fgets(STDIN));
$settingName2 = trim(fgets(STDIN));

// TODO: Create a Config instance

// TODO: Set the first setting to the given value

// TODO: Print whether the first setting exists ("exists" or "missing")

// TODO: Print the value of the first setting

// TODO: Print the current count of settings

// TODO: Use unset() to remove the first setting

// TODO: Print whether the first setting exists now ("exists" or "missing")

// TODO: Print the value of the second setting (which was never set)

?>