Countable 接口

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

简介

类实现 Countable 可被用于 count() 函数.

接口摘要

interface Countable {

/* 方法 */

abstract public count(): int

}


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

?>

down

Rudiger ¶

2 years ago


Unlike an array, an object of a class that implements Countable and has 0 elements is not considered empty:

class C implements Countable {
    public function count() {
        return 0;
    }
}

$a = [];
var_dump($a);
echo 'array is empty: '; var_dump(empty($a));

$c = new C;
var_dump($c);
echo 'Countable is empty: ' ; var_dump(empty($c));

Output:
array(0) {
}
array is empty: bool(true)
object(C)#1 (0) {
}
Countable is empty: bool(false)

down

adam at adamhahn dot com ¶

5 years ago


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.

down

Anonymous ¶

11 years ago


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.

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官方地址：https://www.php.net/manual/en/class.countable.php

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Countable 接口

简介

接口摘要

目录

User Contributed Notes 4 notes