I was diving into Symfony framework (version 4) code and found this piece of code:
$env = $_SERVER['APP_ENV'] ?? 'dev';
I'm not sure what this actually does but I imagine that it expands to something like:
$env = $_SERVER['APP_ENV'] != null ? $_SERVER['APP_ENV'] : 'dev';
Or maybe:
$env = isset($_SERVER['APP_ENV']) ? $_SERVER['APP_ENV'] : 'dev';
Does someone have any precision about the subject?
EDIT:
To all the people who marked my question as negative because there's already a similar question (PHP ternary operator vs null coalescing operator):
It is true that both questions are very similar. However it is hard for everybody to imagine that the "??" is called the coalescing operator.
Otherwise I could easy find it on the official documentation:
http://php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op
However, for someone who didn't know that this feature was added in php 7 it's more likely to type:
"php ?? operator" or "php double question mark operator"
And here is why my question has an added value.
This question is related to
php
operator-keyword
$myVar = $someVar ?? 42;
Is equivalent to :
$myVar = isset($someVar) ? $someVar : 42;
For constants, the behaviour is the same when using a constant that already exists :
define("FOO", "bar");
define("BAR", null);
$MyVar = FOO ?? "42";
$MyVar2 = BAR ?? "42";
echo $MyVar . PHP_EOL; // bar
echo $MyVar2 . PHP_EOL; // 42
However, for constants that don't exist, this is different :
$MyVar3 = IDONTEXIST ?? "42"; // Raises a warning
echo $MyVar3 . PHP_EOL; // IDONTEXIST
Warning: Use of undefined constant IDONTEXIST - assumed 'IDONTEXIST' (this will throw an Error in a future version of PHP)
Php will convert the non-existing constant to a string.
You can use constant("ConstantName")
that returns the value of the constant or null if the constant doesn't exist, but it will still raise a warning. You can prepended the function with the error control operator @
to ignore the warning message :
$myVar = @constant("IDONTEXIST") ?? "42"; // No warning displayed anymore
echo $myVar . PHP_EOL; // 42
$x = $y ?? 'dev'
is short hand for x = y if y is set, otherwise x = 'dev'
There is also
$x = $y =="SOMETHING" ? 10 : 20
meaning if y equals 'SOMETHING' then x = 10, otherwise x = 20
Source: Stackoverflow.com