Comparison

Use identical comparison

Bad:
The simple comparison will convert the string in an integer.

$a = '42';
$b = 42;

if ($a != $b) {
    // The expression will always pass
}

The comparison $a != $b returns FALSE but in fact it's TRUE! The string 42 is different than the integer 42.

Good:
The identical comparison will compare type and value.

$a = '42';
$b = 42;

if ($a !== $b) {
    // The expression is verified
}

The comparison $a !== $b returns TRUE.

Null coalescing operator

Null coalescing is a new operator introduced in PHP 7. The null coalescing operator ?? has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with isset(). It returns its first operand if it exists and is not null; otherwise it returns its second operand.

Bad:

if (isset($_GET['name'])) {
    $name = $_GET['name'];
} elseif (isset($_POST['name'])) {
    $name = $_POST['name'];
} else {
    $name = 'nobody';
}

Good:

$name = $_GET['name'] ?? $_POST['name'] ?? 'nobody';