Ternary, null coalescing and nullsafe operators

Choosing between two values

Often you just need one value or another: "in stock" or "sold out", "item" or "items". Writing a full if / else for that is a lot of lines. The ternary operator does it in one expression:

<?php
$stock = 0;
$label = $stock > 0 ? "In stock" : "Sold out";
echo $label . "\n";

$count = 1;
echo "You have $count " . ($count === 1 ? "item" : "items") . "\n";

Sold out
You have 1 item

The form is condition ? valueIfTrue : valueIfFalse. It is an expression, so you can assign it, print it or pass it to a function. Put brackets around it when it sits inside a longer expression, as in the second example; without them, the . concatenation would bind to the condition first.

Do not nest ternaries. $a ? $b : ($c ? $d : $e) is legal with brackets but hard to read, and PHP 8 refuses the unbracketed form altogether. Use match or if instead.

The short ternary ?:

Leaving out the middle part, a ?: b, gives "a if it is truthy, otherwise b". It is sometimes called the Elvis operator:

<?php
$nickname = "";
echo ($nickname ?: "Guest") . "\n";

$discount = 0;
echo ($discount ?: "no discount") . "\n";

Guest
no discount

That is handy for empty strings, but notice the second line: a discount of 0 is treated as "nothing", because 0 is falsy. When 0 is a valid value, you want the next operator.

Null coalescing ??

a ?? b returns a if it exists and is not null, otherwise b. Two things make it special. It only looks at null, not at other falsy values. And it does not complain when a is an undefined variable or a missing array key, which makes it perfect for optional input:

<?php
$query = ['sort' => 'price'];   // imagine this came from the URL

$sort = $query['sort'] ?? 'name';
$page = $query['page'] ?? 1;
$discount = 0;

echo "sort=$sort page=$page\n";
var_dump($discount ?? 5);
var_dump($missingVariable ?? "default");

sort=price page=1
int(0)
string(7) "default"

Compare that with reading $query['page'] directly, which would raise an "Undefined array key" warning. You will see $_GET['x'] ?? '' and $_POST['x'] ?? '' in almost every form handler.

?? can be chained, and the first value that is set wins:

<?php
$config = ['currency' => null];
$userCurrency = null;

echo ($userCurrency ?? $config['currency'] ?? 'INR') . "\n";

INR

Assign a default with ??=

??= assigns only if the variable or key is missing or null. It is a short way to fill in defaults:

<?php
$options = ['limit' => 20];
$options['limit'] ??= 10;
$options['order'] ??= 'newest';

print_r($options);

Array
(
    [limit] => 20
    [order] => newest
)

The existing limit was kept; the missing order was added.

The nullsafe operator ?->

Objects (covered in the object-oriented section) are reached with ->. If the object might be null, calling -> on it throws an error. The nullsafe operator ?->, added in PHP 8, returns null instead and skips the rest of the chain:

<?php
class Address
{
    public function __construct(public string $city) {}
}

class Customer
{
    public function __construct(public ?Address $address = null) {}
}

$withAddress = new Customer(new Address("Mumbai"));
$withoutAddress = new Customer();
$nobody = null;

var_dump($withAddress->address?->city);
var_dump($withoutAddress->address?->city);
var_dump($nobody?->address?->city);
echo ($withoutAddress->address?->city ?? "No city on file") . "\n";

string(6) "Mumbai"
NULL
NULL
No city on file

Combining ?-> with ??, as in the last line, gives a fallback when anything along the chain is missing.

Which one when

Common mistakes

• Using ?: where 0 or "0" are valid values, so they are replaced by the default. Use ??.
• Using ?? and expecting it to catch empty strings. "" ?? "x" is "", because an empty string is not null.
• Nesting ternaries instead of using match or if.
• Forgetting brackets around a ternary inside a string concatenation.

Exercise

A search page receives optional parameters in an array $query. Read q (default empty string), page (default 1, but keep 0 if sent), and perPage (default 20 if missing or if it is empty or 0). Test with $query = ['q' => 'mug', 'page' => 0, 'perPage' => ''].

<?php
$query = ['q' => 'mug', 'page' => 0, 'perPage' => ''];

$q = $query['q'] ?? '';
$page = $query['page'] ?? 1;
$perPage = ($query['perPage'] ?? null) ?: 20;

echo "q=$q page=$page perPage=$perPage\n";

q=mug page=0 perPage=20