可变数量的参数列表

PHP

• PHP 在用户自定义函数中支持可变数量的参数列表。在 PHP 5.6 及以上的版本中，由 ... 语法实现；在 PHP 5.5 及更早版本中，使用函数 func_num_args()，func_get_arg()，和 func_get_args() 。
• In PHP 5.6 and later, argument lists may include the ... token to denote that the function accepts a variable number of arguments. The arguments will be passed into the given variable as an array; for example:

<?php
function sum(...$numbers) {
    $acc = 0;
    foreach ($numbers as $n) {
        $acc += $n;
    }
    return $acc;
}
echo sum(1, 2, 3, 4);//10
?>

• You can also use ... when calling functions to unpack an array or Traversable variable or literal into the argument list:

<?php
function add($a, $b) {
    return $a + $b;
}
echo add(...[1, 2])."\n";//3
$a = [1, 2];
echo add(...$a);//3
?>

• You may specify normal positional arguments before the ... token. In this case, only the trailing arguments that don't match a positional argument will be added to the array generated by ....
• It is also possible to add a type hint before the ... token. If this is present, then all arguments captured by ... must be objects of the hinted class.

<?php
function total_intervals($unit, DateInterval ...$intervals) {
    $time = 0;
    foreach ($intervals as $interval) {
        $time += $interval->$unit;
    }
    return $time;
}
$a = new DateInterval('P1D');
$b = new DateInterval('P2D');
echo total_intervals('d', $a, $b).' days';
// This will fail, since null isn't a DateInterval object.
echo total_intervals('d', null);
?>

3 days
Catchable fatal error: Argument 2 passed to total_intervals() must be an instance of DateInterval, null given, called in - on line 14 and defined in - on line 2

Finally, you may also pass variable arguments by reference by prefixing the ... with an ampersand (&).

Older versions of PHP

• No special syntax is required to note that a function is variadic; however access to the function's arguments must use func_num_args(), func_get_arg() and func_get_args().
• The first example above would be implemented as follows in PHP 5.5 and earlier:

<?php
function sum() {
    $acc = 0;
    foreach (func_get_args() as $n) {
        $acc += $n;
    }
    return $acc;
}
echo sum(1, 2, 3, 4);//10
?>

func_num_args

func_num_args — Returns the number of arguments passed to the function

func_num_args ( void ) : int

• Gets the number of arguments passed to the function.
• This function may be used in conjunction with func_get_arg() and func_get_args() to allow user-defined functions to accept variable-length argument lists.

func_get_arg

func_get_arg — 返回参数列表的某一项

func_get_arg ( int $arg_num ) : mixed

• 从用户自定义函数的参数列表中获取某个指定的参数。
• 该函数可以配合 func_get_args() 和 func_num_args() 一起使用，从而使得用户自定义函数可以接受自定义个数的参数列表。
• 参数
  arg_num
  参数的偏移量。函数的参数是从0开始计数的。
• 返回值
  返回指定的参数，错误则返回 FALSE

func_get_args

func_get_args — 返回一个包含函数参数列表的数组

func_get_args ( void ) : array