PHP variable length arguments?

Question

In Python and others, there's special syntax for variable length argument lists:

def do_something(*args):
    # do something

do_something(1, 2, 3, 4, 5, ...) # arbitrarily long list

I was reading the PHP manual, and it said this:

PHP 4 and above has support for variable-length argument lists in user-defined functions. This is really quite easy, using the func_num_args(), func_get_arg(), and func_get_args() functions.

No special syntax is required, and argument lists may still be explicitly provided with function definitions and will behave as normal.

I get the first part. You can pass as many arguments as you'd like to a function that takes no arguments, then get them as an array using func_get_args(), etc. I don't really get what the second part is saying, though.

So, my question is, is there some special syntax for variable length arguments, or some best practice that I don't know about? The approach that the manual suggests seems kludgey at best and makes your function seem like it's taking no arguments (unless I'm doing it wrong). Should I not be trying to use this language feature at all?

Answer 1

Here is a more realistic example:

function Average()
{
    $result = 0;
    $arguments = func_get_args();

    foreach ($arguments as $argument)
    {
        $result += $argument;
    }

    return ($result / max(1, func_num_args()));
}

Average(1, 2, 3, 4, 5); // 3

This is called a variadic function.

Answer 2

Unlike Python's * operator or C#'s params keyword, in PHP you don't even have to specify the variable length arguments. As the second part starts off, "No special syntax is required."

As to the rest of the second paragraph: if you want to specify any required or unrelated arguments that come before the variable-length arguments, specify them in your function signature so your function can handle those. Then to get the variable-length arguments, remove the required variables from func_get_args(), like so:

function func($required) {
    // Contains all arguments that come after $required
    // as they were present at call time
    $args = array_slice(func_get_args(), 1);
}

You don't have to do this (you can still slice from func_get_args() and use its different elements accordingly), but it does make your code more self-documenting.

Answer 3

Since PHP 5.6, a variable argument list can be specified with the ... operator.

function do_something($first, ...$all_the_others)
{
    var_dump($first);
    var_dump($all_the_others);
}

do_something('this goes in first', 2, 3, 4, 5);

#> string(18) "this goes in first"
#>
#> array(4) {
#>   [0]=>
#>   int(2)
#>   [1]=>
#>   int(3)
#>   [2]=>
#>   int(4)
#>   [3]=>
#>   int(5)
#> }

As you can see, the ... operator collects the variable list of arguments in an array.

If you need to pass the variable arguments to another function, the ... can still help you.

function do_something($first, ...$all_the_others)
{
    do_something_else($first, ...$all_the_others);
    // Which is translated to:
    // do_something_else('this goes in first', 2, 3, 4, 5);
}

---

Since PHP 7, the variable list of arguments can be forced to be all of the same type too.

function do_something($first, int ...$all_the_others) { /**/ }

Answer 4

There's no special syntax for variable length argument functions.

Simply use the func_num_args() and func_get_args() functions to get the arguments.

Example:

function callMe(){

    if(func_num_args() == 0){
        echo 'No arguments =)';
    }else{
        var_dump(func_get_args());
    }

}

Answer 5

The second portion is basically saying that once you start using the variable argument functions, then

function average() { ... }
function average(arg1, arg2, arg3) { ... }

work identically, just that the second version has 3 arguments explicity listed. That's all, don't try to read more into a man page than there is.

Answer 6

I usually do this to avoid kept changing function, and avoid error on argument order

function any_function($ops=array())
{
}

$ops = array('name'=>1, 'type'=>'simplexml', 'callback'=>...);