PHP/function variable
About
A variable can store a reference to a function, which can then be called from the variable.
Named Functions/Methods
The thing that isn't explained very well in the documentation is that if you want to assign a predefined function to a variable, you just use a string which is a callable/accessible form of the function.
function Example1() { echo "Example1 was called!\n"; }
#$fEx1 = Example1; // does not work; sees "Example1" as a constant
$fEx1 = 'Example1';
$fEx1(); // prints "Example1 was called!"
class cExample2 {
static public function Test1() { echo "Test1 was called!\n"; }
}
#$fEx2 = cExample2::Test1; // does not work; sees "Test1" as a class constant
$fEx2 = 'cExample2::Test1';
$fEx2(); // prints "Test1 was called!"
The variable can be used to call the function in exactly the same way as if it had been assigned an anonymous function.
Anonymous Functions
$fEx3 = function() { echo "Anonymous function was called!\n"; };
$fEx3(); // prints "Anonymous function was called!"
Unlike with predefined functions, however, the type for the variable is Callable rather than string.
Functions as Function Parameters
If you declare a function parameter as Callable, that parameter will still accept as string argument, and that argument will remain as a string (i.e. will not be converted to Callable).
The following code, run after the above examples, illustrates this:
function TestFunc2(Callable $f) {
echo 'Calling the function: ';
$f();
echo 'Type for f: '.gettype($f)."\n";
}
TestFunc2($fEx3);
TestFunc2($fEx2);
Output:
Example1 was called!
Test1 was called!
Anonymous function was called!
Calling the function: Anonymous function was called!
Type for f: object
Calling the function: Test1 was called!
Type for f: string