Stringable

Stringable is a type, which represents variables that may be used as as string : either a string, a heredoc or a string constant; or an object which has the __toString() method.

Stringable is automatically added to any class (and subclass) that has the __toString() method, though it is recommended to add it explicitly.

<?php

function foo(stringable $s) {
     print $s;
}

?>

Documentation

See also What is Stringable Interface in PHP 8?

Related : String

Added in PHP 8.0