Date and time handling

1. Standard datetime format

• Use ISO8601 for both frontend and backend when exchanging datetime data
• Example: 2025-05-02T15:30:00+07:00

2. Register CarbonImmutable globally

Date::use(CarbonImmutable::class);

3. Use the application timezone by default

Laravel sets PHP's default timezone from config('app.timezone') during bootstrap. Do not pass that same config value to Carbon methods such as now(), parse(), or createFromFormat(). Pass a timezone only when the operation explicitly needs a timezone different from the application's default.

4. Type hinting datetime parameters

• Use CarbonInterface when you need Carbon's utility API
• Use DateTimeInterface for simpler cases

public function handleViaCarbon(CarbonInterface $when): void {}
public function logCreatedAt(DateTimeInterface $timestamp): void {}

5. Why use CarbonImmutable

Problem with Carbon (mutable)	How CarbonImmutable helps
$dt->addDay() mutates the original $dt	Methods return a new instance
Side effects are hard to debug	Immutability makes behavior predictable
setTimezone() can have broad impact	No side effects

$expiresAt = Carbon::now();
$expiresAt->addMinutes(5); // mutates $expiresAt

$expiresAt = CarbonImmutable::now();
$expiresAt->addMinutes(5); // $expiresAt unchanged

6. Casting in Eloquent models

protected function casts(): array
{
    return [
        'created_at' => 'immutable_datetime',
        'updated_at' => 'immutable_datetime',
        'delivery_date' => 'immutable_datetime',
    ];
}

Note

• Use the immutable_datetime cast (Laravel 10+)
• Add PHPDoc so IDEs and PHPStan can check types accurately