PHP 8.5 Property Hooks: Practical Examples

PHP 8.5 introduces property hooks: get and set blocks attached directly to a property declaration. Before hooks, validation and transformation on read/write required either __get/__set magic methods (which apply globally and need extra bookkeeping) or explicit getX()/setX() methods (which are verbose and break direct property access syntax).

A set hook receives the incoming value as $value and can validate or transform it before storing. A get hook runs on read and can compute a derived value. Properties with only a get hook have no backing storage at all. Asymmetric visibility (public private(set)) is a related feature that makes a property publicly readable but writable only from within the class, enforced at the engine level without any hook code needed.

<?php

/**
 * PHP 8.5 property hooks: get and set hooks replace
 * the verbose getProp() / setProp() pattern.
 *
 * Requires PHP 8.5+
 */
class Temperature
{
    // Hook on set: validate and convert
    public float $celsius {
        get => $this->celsius;
        set {
            if ($value < -273.15) {
                throw new ValueError("Temperature below absolute zero: $value");
            }
            $this->celsius = round($value, 2);
        }
    }

    // Computed property via get hook (no backing storage)
    public float $fahrenheit {
        get => $this->celsius * 9/5 + 32;
    }

    public float $kelvin {
        get => $this->celsius + 273.15;
    }

    public function __construct(float $celsius)
    {
        $this->celsius = $celsius;
    }
}

$t = new Temperature(100.0);
printf("Celsius:    %.2f\n", $t->celsius);    // 100.00
printf("Fahrenheit: %.2f\n", $t->fahrenheit); // 212.00
printf("Kelvin:     %.2f\n", $t->kelvin);     // 373.15

$t->celsius = 0.0;
printf("\nAfter setting to 0C:\n");
printf("Fahrenheit: %.2f\n", $t->fahrenheit); // 32.00

// Validation
try {
    $t->celsius = -300.0;
} catch (ValueError $e) {
    echo "\nCaught: " . $e->getMessage() . "\n";
}

// Asymmetric visibility (public read, private write from inside)
class BankAccount
{
    public private(set) float $balance = 0.0;

    public function deposit(float $amount): void
    {
        if ($amount <= 0) throw new ValueError("Deposit must be positive");
        $this->balance += $amount; // allowed: same class
    }

    public function withdraw(float $amount): void
    {
        if ($amount > $this->balance) throw new RuntimeException("Insufficient funds");
        $this->balance -= $amount;
    }
}

$account = new BankAccount();
$account->deposit(1000.0);
$account->withdraw(250.0);
printf("\nBalance: %.2f\n", $account->balance); // 750.00

// Cannot write from outside:
try {
    $account->balance = 99999.0;
} catch (Error $e) {
    echo "Caught: " . $e->getMessage() . "\n";
}