PHP 7 has significantly improved overall performance. Indeed there are major features such as null coalescing operator or return type declarations. You should definitely check PHP documentation if you do not know them.

Here are less known features that might be useful.

Same namespace, same use

Before PHP 7 developers used to do :

use Universe\Saiyan;
use Universe\SuperSaiyan;

Since PHP 7 :

use Universe\{Saiyan, SuperSaiyan};

It's the same for functions and constants. You can group them if they belong to the same namespace.

Constants can be arrays

define('NAMES', [
    'first'  => 'John',
    'middle' => 'Fitzgerald',
    'last'   => 'Kennedy'
]);

echo NAMES['last']; //displays "Kennedy"

Spaceship Operator

It's written like that <=>. It combines comparisons. It stands for " less than, equal to or greater than". It's really useful when using user-defined comparison functions to sort arrays because of the return values :

• 0 if values are equal
• 1 if value on the left is greater
• -1 if the value on the right is greater

source

So let's sort the following array of actresses :

$actressesWithAcademyAwards = [
    [ 'name' => 'Katharine Hepburn', 'awards' => 4 ],
    [ 'name' => 'Jessica Lange', 'awards' => 2 ],
    [ 'name' => 'Meryl Streep', 'awards' => 3 ],
    [ 'name' => 'Cate Blanchett', 'awards' => 2 ],
];

Instead of writing multiple lines to make the comparisons you can do it in 1 line :

usort($actressesWithAcademyAwards, function ($a, $b) {
    return $a['awards'] <=> $b['awards'];
});

print_r($actressesWithAcademyAwards);

this returns :

Array
(
    [0] => Array
        (
            [name] => Jessica Lange
            [awards] => 2
        )

    [1] => Array
        (
            [name] => Cate Blanchett
            [awards] => 2
        )

    [2] => Array
        (
            [name] => Meryl Streep
            [awards] => 3
        )

    [3] => Array
        (
            [name] => Katharine Hepburn
            [awards] => 4
        )
)

It's a very common PHP routine so the spaceship operator saves time. Besides it's more readable imho.

First / last key of array (PHP 7.3)

Since PHP 7.3 you can easily get the first and the last key of an array :

$array = [ 'v' => 1, 'i' => 2, 'p' => 3 ];

$firstKey = array_key_first($array);
$lastKey = array_key_last($array);

print_r($firstKey); // v
print_r($lastKey); // p

Really clean because it does not affect the internal array pointer.

Spread operator in array (PHP 7.4)

This feature allows the following :

$abc = range('a', 'c');
$def = range('d', 'f');
$ghi = range('g', 'i');
$all = [...$abc, ...$def, ...$ghi, 'j'];
print_r($all);

you get :

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
    [5] => f
    [6] => g
    [7] => h
    [8] => i
    [9] => j
)

It basically replaces array_merge() in most cases.

Arrow functions (PHP 7.4)

Be careful, for now it's meant for short closures with only one expression (hence the word "short") :

$c = 3;
$addC = fn($x) => $x + $c;
echo $addC(70); // 73

No need for use keyword.

source

Constant visibility (PHP7.1)

class Mother {
    private const ERROR_LEVEL_1 = 'achtung';
}

Visibility is useful to make sure things that should not be overwritten aren’t. Before PHP 7.1 this was not possible for class constants (always public).

source

Wrap up

PHP 7 is powerful. It's faster and it comes with great features. Did you know all these stuffs PHP 7 can do ?