Is passing variables to php anonymus function without use legit? - php

Question

I just learned about php anonymous functions and found out that the following code is correct:
Example1:
//$mysqli = new mysqli(...)
(function($x, $y, $conn) {
echo $x, $y; //$x and $y are not visible outside
})(786, 333, $mysqli);
Over the internet I have found examples like
Example2:
$x = 786; $y = 333;
(function($x, $y) {
echo $x, $y;
})();
Or
Example3:
$x = 786; $y = 333;
(function() use($x, $y){
echo $x, $y;
})();
I couldn't find any php documentation or code on stackoverflow which suggest example1 is correct syntax. Please tell me with official reference if example1 like syntax is allowed in php.

Answer 1

The first example is effectively defining the function and then calling it with the values. Something like...
(definition of function)(values to pass);
You can split into two parts to show how this works...
$fn =function($x, $y, $conn) {
echo $x, $y; //$x and $y are not visible outside
};
($fn)(786, 333, $mysqli);

Answer 2

//$mysqli = new mysqli(...)
(function($x, $y, $conn) {
echo $x, $y; //$x and $y are not visible outside
})(786, 333, $mysqli);
This is perfectly valid, and just follows from two things:
The function(...) { ... } syntax creates and returns a Closure object
A Closure object can be invoked directly as though it was a function name
There is no special syntax, it's just one of an infinite number of ways you can put the building blocks of PHP together.
There are lots of other combinations you can do for the same reason, e.g.:
class Foo
public static function make_function() {
return function($x, $y, $conn) {
echo $x, $y;
};
}
}
(Foo::make_function())(786, 333, $mysqli);
But also:
class Foo
public static function make_function($conn) {
return function($x, $y) use ($conn) {
echo $x, $y;
};
}
}
(Foo::make_function($conn))(786, 333, $mysqli);
As with your example, specifying a use clause doesn't make much difference in this specific case because we're executing the function straight away. But it allows you to "capture" a value in one place and then pass the other arguments later, e.g.
class Foo
public static function make_function($conn) {
return function($x, $y) use ($conn) {
echo $x, $y;
};
}
}
$f = Foo::make_function($mysqli);
// later...
$f(786, 333);