Интерфейс Countable
(PHP 5 >= 5.1.0, PHP 7)
Введение
Классы, которые реализуют интерфейс Countable, могут быть использованы с функцией count().
Обзор интерфейсов
Содержание
- Countable::count — Количество элементов объекта
(PHP 5 >= 5.1.0, PHP 7)
Классы, которые реализуют интерфейс Countable, могут быть использованы с функцией count().
Коментарии
I just want to point out that your class has to actually implement the Countable interface, not just define a count method, to be able to use count($object) and get the expected results. I.e. the first example below won't work as expected, the second will. (The normal arrow function accessor ($object->count()) will work fine, but that's not the kewl part :) )
<?php
//Example One, BAD :(
class CountMe
{
protected $_myCount = 3;
public function count()
{
return $this->_myCount;
}
}
$countable = new CountMe();
echo count($countable); //result is "1", not as expected
//Example Two, GOOD :)
class CountMe implements Countable
{
protected $_myCount = 3;
public function count()
{
return $this->_myCount;
}
}
$countable = new CountMe();
echo count($countable); //result is "3" as expected
?>
Note that arrays don't implement countable. Therefore you can't force a countable parameter for a function if you want it also to work with native arrays.When using GMP/BC/Floating-Point Numbers to work with integers larger than PHP_INT_MAX, be aware that using the count() function will typecast the returned value to an integer.
<?php
class counter implements Countable {
public function count() {
// Number of IPv6 addresses in a single /32 IPv6 allocation (2^96)
return "18446744073709551616"; // assume generated/exported by big-int library(GMP/BC/etc.)
}
}
$obj = new counter();
echo $obj->count(); // prints string "18446744073709551616"
echo count($obj); // prints int PHP_INT_MAX
// This is because of the typecasting
echo (int) "18446744073709551616"; // prints int PHP_INT_MAX
?>
This will also cause problems for floating-point values.
<?php
class counter implements Countable {
public function count() {
// Number of IPv6 addresses in a single /32 IPv6 allocation (2^96)
return 18446744073709551616;
}
}
$obj = new counter();
echo $obj->count(); // prints float 18446744073709551616.000000
echo count($obj); // prints int 0
// This is because of the typecasting
echo (int) 18446744073709551616; // prints int 0
?>
This is only problematic when counting higher than PHP_INT_MAX.