Since PHP 7.0 has been released there's more attention on scalar types. Keeping types for data from within your application is relatively simple. But when talking to external systems, like a database things aren't always as one eventually might initially expect.

For MySQL the type we see -- in the first approximation -- is defined by the network protocol. The MySQL network protocol by default converts all data into strings. So if we fetch an integer from the database and use PHP 7's typing feature we get an error:

<?php
declare(strict_types=1);

function getInteger() : int {
  $mysqli = new mysqli(...);
  return $mysqli->query("SELECT 1")->fetch_row()[0];
}

var_dump(getInteger());
?>

Fatal error: Uncaught TypeError: Return value of getInteger() must be of the type integer, string returned in t.php:6

Of course the solution is easy: Either we cast ourselves or we disable the strict mode and PHP will …

So in my blog series I try to cover all additions to PHP trunk so I have to mention scalar type hints.

<?php
function print_float(float $f) {
    echo $f."\n";
}

for ($i = 1; $i < 5; $i++) {
    print_float( $i / 3 );
}
?>
        

0.33333333333333
0.66666666666667

Catchable fatal error: Argument 1 passed to print_float() must be of the type double, integer given, called in typehints.php on line 7 and defined in typehints.php on line 2

Is expected behavior in PHP's trunk. If you want such a thing to work please use the numeric type hint.

In case that wasn't enought fun: There's more!

<?php
function handle_result(int $i) {
    echo $i."\n";
}

$pdo = new PDO("mysql:host=localhost;dbname=test", "user", "pass"); …