While searching for something else, I found this code
$x = "foo";
function foo(){ echo "wtf"; }
$x(); # "wtf"
and when I searched google for this, I got only C results not PHP, while I know that under the PHP hood is C, I would really like some explanation about that.
What is that called?
and how it is interpreted by PHP zend? is it some sort of callable?
and is it still available in PHP 7+ ?
This is called variable functions in PHP : http://php.net/manual/en/functions.variable-functions.php
Basically, when there is a variable before the (), first the variable get resolved and interpreter get the value of it and try to find the function with that value. If the function exists, it calls or function not found exception will be thrown.
It is a callable (variable function: http://php.net/manual/en/functions.variable-functions.php )
Zend just treats it as a callable and calls the function.
It is an old and stable language feature, and still available in PHP7+ (and it will be available as long as possible)
The callable types and normalizations are given in the table below: http://php.net/manual/en/language.types.callable.php#118032
Callable | Normalization | Type
--------------------------------+---------------------------------+--------------
function (...) use (...) {...} | function (...) use (...) {...} | 'closure'
$object | $object | 'invocable'
"function" | "function" | 'function'
"class::method" | ["class", "method"] | 'static'
["class", "parent::method"] | ["parent of class", "method"] | 'static'
["class", "self::method"] | ["class", "method"] | 'static'
["class", "method"] | ["class", "method"] | 'static'
[$object, "parent::method"] | [$object, "parent::method"] | 'object'
[$object, "self::method"] | [$object, "method"] | 'object'
[$object, "method"] | [$object, "method"] | 'object'
A PHP function is passed by its name as a string. under Passing section.A variable function. The variable x is simply holding a value which is equal to function name. Calling variable that way results to calling the function.
