PHP Carbon class changing my original variable value

Question

I'm trying to make a few navigation buttons in a calendar type thing I'm creating, and I'm using carbon to create the dates.

This is the code in the controller:

if ($date == null) {
    $date = \Carbon\Carbon::now();
} else {
    $date = \Carbon\Carbon::createFromFormat('Y-m-d', $date);
}
$navDays = [
    '-7Days' => $date->subDay('7')->toDateString(),
    '-1Day'  => $date->subDay('1')->toDateString(),
    'Today'    => $date->today()->toDateString(),
    '+1Day'  => $date->addDay('1')->toDateString(),
    '+7Days' => $date->addDay('7')->toDateString()
];

and then I'm my view, I'm doing this:

@foreach($navDays as $key => $i)
    <li>
        <a href="/planner/bookings/{{ $i }}" class="small button">
            {{ $key }}
        </a>
    </li>
@endforeach

This problem is, that carbon seems to change the $date during the array creating, because these are the dates I'm getting(with $date being set to 2015-11-29):

<ul class="button-group even-5">
    <li><a href="/planner/bookings/2015-11-22" class="small button">-7Days</a></li>
    <li><a href="/planner/bookings/2015-11-21" class="small button">-1Day</a></li>
    <li><a href="/planner/bookings/2015-12-22" class="small button">Today</a></li>
    <li><a href="/planner/bookings/2015-11-22" class="small button">+1Day</a></li>
    <li><a href="/planner/bookings/2015-11-29" class="small button">+7Days</a></li>
</ul>

Does anybody know what I'm doing wrong?

Meyerhof

Answer 1

When you run these methods against a Carbon object it updates the object itself. Therefore addDay() moves the value of Carbon one day forward.

Here's what you need to do:

$now = Carbon::now();

$now->copy()->addDay();
$now->copy()->addMonth();
$now->copy()->addYear();
// etc...

The copy method essentially creates a new Carbon object which you can then apply the changes to without affecting the original $now variable.

To sum up, the methods for copying a Carbon instance are:

• copy
• clone - an alias of copy

Check out the documentation: https://carbon.nesbot.com/docs/

Comras

As of Laravel +5.8 you can also do $now->toImmutable()->addDay(). – Shingly

@AmirHossein you should add this as a full answer. It's a much cleaner method to work with immutable objects instead of cloning a mutable one. – Unreasonable

Answer 2

The problem is that you're assuming that subDay()/addDay() don't change the date object, whereas they do.... they're just wrapping around the DateTime object modify() method:

DateTime::modify -- date_modify — Alters the timestamp

(my emphasis)

Instead, use

$navDays = [
    '-7Days' => (clone $date)->subDay('7')->toDateString(),
    '-1Day'  => (clone $date)->subDay('1')->toDateString(),
    'Today'  => (clone $date)->today()->toDateString(),
    '+1Day'  => (clone $date)->addDay('1')->toDateString(),
    '+7Days' => (clone $date)->addDay('7')->toDateString()
];

Millian

this gives me an error: syntax error, unexpected '->' (T_OBJECT_OPERATOR), expecting ']' Do i need to set these before hand, and then add them to the array? – Chrischrism

Sorry, realised that I'd tested while in my php7 environment and didn't think that it wouldn't work with PHP5 – Millian

carbon also has a copy method so you can do something like.. $date->copy()->subDay('7')->toDateString() – Amie

php.net/manual/en/class.datetime.php vs php.net/manual/en/class.datetimeimmutable.php. Carbon is based on the first – Maidie

Answer 3

Doco says

You can also create a copy() of an existing Carbon instance. As expected the date, time and timezone values are all copied to the new instance.

$dt = Carbon::now();
echo $dt->diffInYears($dt->copy()->addYear());  // 1

// $dt was unchanged and still holds the value of Carbon:now()

Degenerate