Question

I need to know, how much arguments a function accepts (including optional args). w/o calling that function and w/o getting errors. Like I can check with is_callable before I call a function in order to not get php error.
For example, in javascript every function have a length property:

Math.sin.length == 1
Array.prototype.slice.length == 2

I know, this will return only declared arguments, but there’s no support for optional arguments with default values in js syntax.

Is there a similar thing in php?
Working in php 5.2+ is enough. Wroking for only global functions (not methods) is also enough.
Hackish solutions like trying to call function with 0 args, then with 1 arg… are highly discouraged, cause function call cost may be very high.

Answer 1

Use ReflectionFunction:

function a($b, $c = 1) {
    echo $b, $c;
}

$rf = new ReflectionFunction('a');
echo $rf->getNumberOfParameters();

In PHP 5.3, ReflectionFunction supports closures:

$a = function($b, $c = 1) {
    echo $b, $c;
};

$rf = new ReflectionFunction($a);
echo $rf->getNumberOfParameters();