Countable 接口
目录
- Countable::count — 统计一个对象的元素个数
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User Contributed Notes 4 notes
isaac dot z dot foster dot nada at spamporfav dot gmail dot com ¶
12 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
?>
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)
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.