Nested Ternary Operators Requires Explicit Parentheses in PHP 8.0

The ternary (?:) operator is a conditional operator that allows to shorten if/else structures and decrease the length of code. The syntax for ternary operator can be represented as follows:

condition ? expression1 : expression2

• condition - is an expression that evaluates to a boolean value (true or false).
• expression1 - is an expression that will be evaluated if condition is true.
• expression2 - is an expression that will be evaluated if condition is false.

Let's say we have if/else structure like this:

<?php

$number = 10;
if ($number % 2 === 0) {
    $result = 'Even';
} else {
    $result = 'Odd';
} 

This code snippet can be rewritten as follows:

<?php

$number = 10;
$result = $number % 2 === 0 ? 'Even' : 'Odd';

PHP allows using nested ternary operators. These operators are left-associative instead of right-associative. It can be very confusing. So, in PHP 7.4 using nested ternary operators without explicit parentheses emits a deprecation warning.

Let's say we have the following code snippet:

<?php

$number = 10;
echo $number > 0 ? 'Positive' : $number < 0 ? 'Negative' : 'Zero';

In PHP 7.4 we will get a deprecation warning and the code prints Negative instead of Positive because ternary operator is left-associative:

Deprecated: Unparenthesized `a ? b : c ? d : e` is deprecated. Use either `(a ? b : c) ? d : e` or `a ? b : (c ? d : e)` in main.php on line 4
Negative

Since PHP 8.0, the nested ternary operators require explicit parentheses and using without them, a fatal error occurs.

If we run the previous code snippet in PHP 8.0 or newer versions, we will get a fatal error:

Fatal error: Unparenthesized `a ? b : c ? d : e` is not supported. Use either `(a ? b : c) ? d : e` or `a ? b : (c ? d : e)` in main.php on line 4

Code snippet can be rewritten as follows:

<?php

$number = 10;
echo $number > 0 ? 'Positive' : ($number < 0 ? 'Negative' : 'Zero');

Output:

Positive