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 */
    public count(): int
    }

    目录

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    用户贡献的备注 3 notes

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    48
    isaac dot z dot foster dot nada at spamporfav dot gmail dot com
    14 years ago
    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
    ?>
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    4
    adam at adamhahn dot com
    7 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.
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    1
    Anonymous
    13 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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