问题
With the release of a new PHP version, PHP 7, new features are introduced. among these new features is an operator I am not familiar with. The Null coalesce operator.
What is this operator and what are some good use cases?
回答1:
You can use it to init a variable that might be null
The ?? operator is called the null-coalescing operator. It returns the left-hand operand if the operand is not null; otherwise it returns the right hand operand.
Source: https://msdn.microsoft.com/nl-nl/library/ms173224.aspx
(not dependent on language)
Use case
You can write
$rabbits;
$rabbits = count($somearray);
if ($rabbits == null) {
$rabbits = 0;
}
You can use the shorter notation
$rabbits = $rabbits ?? 0;
回答2:
According to the PHP Manual:
The null coalesce operator (??) has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with isset(). It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.
// Fetches the value of $_GET['user'] and returns 'nobody'
// if it does not exist.
$username = $_GET['user'] ?? 'nobody';
// This is equivalent to:
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';
// Coalesces can be chained: this will return the first
// defined value out of $_GET['user'], $_POST['user'], and
// 'nobody'.
$username = $_GET['user'] ?? $_POST['user'] ?? 'nobody';
回答3:
$username = $_GET['user'] ?? 'nobody';
is same as
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';
?? is ternary shorthand
来源：https://stackoverflow.com/questions/33666256/what-is-the-null-coalesce-operator-used-for