Note: empty array is converted to null by non-strict equal '==' comparison. Use is_null() or '===' if there is possible of getting empty array.
$a = array();
$a == null <== return true
$a === null < == return false
is_null($a) <== return false
Le type null est le type unité de PHP, c'est-à-dire qu'il n'a qu'une seule valeur:
null.
Les variables non définies et les variables unset() auront la valeur null.
Il y a une seule valeur de type null, et c'est la constante
insensible à la casse null.
<?php
$var = NULL;
?>null
Cette fonctionnalité est OBSOLÈTE à partir de PHP 7.2.0, et SUPPRIMÉE à partir de PHP 8.0.0. Dépendre de cette fonctionnalité est fortement déconseillé.
Transtyper une variable vers null en utilisant
la syntaxe (unset) $var n'effacera pas
la variable, ni écrasera sa valeur. Ca ne fera que retourner
la valeur null.
Note: empty array is converted to null by non-strict equal '==' comparison. Use is_null() or '===' if there is possible of getting empty array.
$a = array();
$a == null <== return true
$a === null < == return false
is_null($a) <== return falseNULL is supposed to indicate the absence of a value, rather than being thought of as a value itself. It's the empty slot, it's the missing information, it's the unanswered question. It's not a jumped-up zero or empty set.
This is why a variable containing a NULL is considered to be unset: it doesn't have a value. Setting a variable to NULL is telling it to forget its value without providing a replacement value to remember instead. The variable remains so that you can give it a proper value to remember later; this is especially important when the variable is an array element or object property.
It's a bit of semantic awkwardness to speak of a "null value", but if a variable can exist without having a value, the language and implementation have to have something to represent that situation. Because someone will ask. If only to see if the slot has been filled.