1.2.1320. Use Contravariance

Contravariance is compatible argument typehint. A child class may accept an object of a parent class of the argument type of its parent’s method.

Since a children class may accept a parent class of the argument type, the evolution is in opposite order.

Contravariance is a PHP 7.4 feature. Contravariance is distinct from return type covariance.

<?php
class X {
  function m(Y $z): X {}
}

// m is overwriting the parent's method.
// The return type is different.
// The return type is compatible, as Y is also a sub-class of X.
class Y extends X {
  function m(X $z): Y {}
}

?>

See also Covariant Returns and Contravariant Parameters and No title for `Php/UseCovariance <No anchor for Php/UseCovariance>`.

1.2.1320.1. Specs

Short name	Php/UseContravariance
Rulesets	All, Appinfo, CE
Exakat since	1.9.3
PHP Version	With PHP 7.4 and more recent
Severity	Minor
Time To Fix	Quick (30 mins)
Precision	Very high
Features	type-covariance, type-contravariance
Available in	Entreprise Edition, Community Edition, Exakat Cloud