Php Null coalescing operator

Question

I am trying to understand how the null coalescing operator does really work. So, I tested many examples after reading the documentation in php.net and some posts on stackoverflow.

However, I can't understand this code:

<?php 
$x = false ?? 'stackoverflow';
var_dump($x); // bool(false)

since it's equivalent to (from php.net#null-coalescing)

isset(false) ? false : 'stackoverflow';

and since isset(false) generates a fatal error.

Could, please, someone explain to me?

from the docs: "In particular, this operator does not emit a notice if the left-hand side value does not exist, just like isset(). This is especially useful on array keys." — Kaddath
– Kaddath, Commented May 17, 2018 at 13:55
Like it says, it's syntactic sugar for a common use-case of using a ternary operator in conjunction with isset. If that's not what you're doing, this isn't the operator you need. The docs could possibly be worded a little better, in fairness. — iainn
– iainn, Commented May 17, 2018 at 13:55
Note that it is named the "Null Coalescing Operator", not the "False Coalescing Operator". — Sammitch
– Sammitch, Commented May 17, 2018 at 18:06

Kawaljeet Singh · Accepted Answer · 2018-05-17 14:03:42Z

2

Null coalescing operator returns its first operand if it exists and is not NULL;

Otherwise it returns its second operand.

In your case first operand is false so it is assigned to the variable. For e.g; if you initialize null to first operand then it will assign second operands value as shown.

 $a = null;
 $x = $a ?? 'abc';
 var_dump($x);

Result :
string(3) "abc"

edited May 17, 2018 at 14:03

answered May 17, 2018 at 13:58

Kawaljeet Singh

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