1.2.970. Php 8.0 Only TypeHints

Three scalar typehints are introduced in version 8.0. They are mixed, false and null.

false represents a false boolean, and nothing else. It is more restrictive than a boolean, which accepts true too. null is an alternative syntax to ? : it allows the type to be null. mixed is an special typehint which explicitly means any type.

An interface stringable was also introduced to identify objects that may be turned into a string.

Both the above typehints are to be used in conjunction with other types : they can’t be used alone. In PHP 7.0, both those values could not be used as a class or interface name, to avoid confusion with the actual booleans, nor null value.

<?php

// function accepts an A object, or null.
function foo(A|null $x) {}

// same as above
function foo2(A|null $x) {}

// returns an object of class B, or false
function bar($x) : false|B {}

?>

See also PHP RFC: Union Types 2.0.

1.2.970.1. Specs

Short name	Php/Php80OnlyTypeHints
Rulesets	All, Appinfo, CE, Changed Behavior, CompatibilityPHP56, CompatibilityPHP70, CompatibilityPHP71, CompatibilityPHP72, CompatibilityPHP73, CompatibilityPHP74
Exakat since	2.0.9
PHP Version	All
Severity	Minor
Time To Fix	Quick (30 mins)
Precision	Very high
Features	mixed, false, null
Available in	Entreprise Edition, Community Edition, Exakat Cloud