I like to be as strict as possible when writing PHP, it helps avoid whole classes of bugs. This is achieved in PHP by doing two things: declare(strict_types=1) and type declarations wherever possible.

This isn't a magic bullet. Even with 100% coverage there are type coercions and loose type checks hiding within in the PHP engine.

Switch Statements

<?php

declare(strict_types=1);

switch (true) {
    case 1: echo 'one'; break; // This case is matched
    case true: echo 'true'; break;
}

Ternaries

<?php

declare(strict_types=1);

$a = 1 ? 'true' : 'false'; // $a is 'true'
$b = 0 ? 'true' : 'false'; // $b is 'false'

This also applies to short terneries using the ?: syntax.

Array Sort

<?php

declare(strict_types=1);

$array = ['10', '5', 2, 1];

sort($array); // [1, 2, '5', '10']

Inequalities

<?php

declare(strict_types=1);

0 < true; // true
0 > true; // false
1 >= true; // true
1 <= true; // true
0 >= true; // false
0 <= true; // true

Spaceship Operator

<?php

declare(strict_types=1);

1 <=> true; // 0
0 <=> true; // -1
1 <=> false; // 1
0 <=> false; // 0

Workarounds

To avoid all of the above, I follow some simple rules:

• Never use switch, replace it with match
• When using terneries use explicit strict comparison: $a = (1 === true) ? 'true' : 'false';
• Only sort an array when you can guarantee that all the values are of the same type
• Only use inequalities when both sides are guaranteed to have the same type

If you're wondering how types can be 'guaranteed', PHPStan and code like this:

class Thing
{
    private $values = [];
    
    public function addValue(int $value) {
        $this->values[] = $value;
    }
    
    public function getValues() {
        return $this->values;
    }
}

$thing = new Thing();
$thing->addValue(1);
$thing->addValue(2);

sort($thing->getValues())