PHP: variable-length argument list by reference?

Question 1

Is it possible to create a PHP function that takes a variable number of parameters all of them by reference?

It doesn't help me a function that receives by reference an array of values nor a function that takes its arguments wrapped in an object because I'm working on function composition and argument binding. Don't think about call-time pass-by-reference either. That thing shouldn't even exist.

Question 2

PHP 5.6 introduced new variadic syntax which supports pass-by-reference. (thanks @outis for the update)

function foo(&...$args) {
    $args[0] = 'bar';
}

For PHP 5.5 or lower you can use the following trick:

function foo(&$param0 = null, &$param1 = null, &$param2 = null, &$param3 = null, &$param4 = null, &$param5 = null) {
  $argc = func_num_args();
  for ($i = 0; $i < $argc; $i++) {
    $name = 'param'.$i;
    $params[] = & $$name;
  }
  // do something
}

The downside is that number of arguments is limited by the number of arguments defined (6 in the example snippet). but with the func_num_args() you could detect if more are needed.

Passing more than 7 parameters to a function is bad practice anyway ;)

Question 3

The very last parameter, count, is passed by reference. You can see this in the description at http://us.php.net/str_replace where there's a & in front of the variable.

This means you cannot use a literal 1 there. You'd have to do:

$sql = str_replace('?', "'" . $param . "'", $sql, $count);
echo $count;

You'll now have displayed on the screen how many instances were replaced.

Question 4

After this loop is executed:

foreach ($x as $n => &$v) { }

$v ends up as a reference to $x[2]. Whatever you assign to $v actually gets assigned $x[2]. So at each iteration of the second loop:

foreach ($y as $n => $v) { }

$v (or should I say $x[2]) becomes:

'bye bye'
'world'
'harsh'

Question 5

Let's pretend $x is a piece of paper with 5 written on it.

function sum($y) {
  $y = $y + 5; 
}

Here $y is the value of what you have written. You add 5 to such value in your mind, but the note is left untouched.

function sum(&$y) {
  $y = $y + 5; 
}

With the reference operator (&$y), you pass the very paper to the function, and it overwrites what's written on it.

For primitive values like numbers, I wouldn't bother and always return the value you want:

function valuePlusFive($x) {
  return $x + 5;
}

$x = 5;
$x = valuePlusFive($x);

Question 6

There are no such subroutines in Fortran.

The syntax rule for a subroutine statement in Fortran 2008 is (12.6.2.3, R1235):

[ prefix ] SUBROUTINE subroutine-name [ ( [ dummy-arg-list ] ) [ proc-language-binding-spec ] ]

where dummy-arg-list is a list (in assumed syntax rule terms) of dummy-args. A dummy-arg is (R1235) either a name or a literal *.

[Before we get too excited about the possibility of variadic support, the * refers, of course, to an alternate return indicator.]

A list (R101) still refers to a well-defined (at source time) number of items.

There is a stated restriction regarding interoperability with C, that (15.3.7) the C prototype

... does not have variable arguments as denoted by the ellipsis (...)

Similar arguments apply to (Fortran) functions.

PHP: variable-length argument list by reference?

Answers

php,pass-by-reference,parameter-passing,variadic-functions,function-parameter

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