(PHP 5, PHP 7, PHP 8)
这个接口没有任何方法，它的作用仅仅是作为所有可遍历类的基本接口。
| 版本 | 说明 |
|---|---|
| 7.4.0 | Traversable 接口现在可以由抽象类实现。继承的类必须实现 Iterator 或 IteratorAggregate。 |
注意:
实现此接口的内置类可以使用 foreach 进行遍历而无需实现 IteratorAggregate 或 Iterator 接口。
注意:
在 PHP 7.4.0 之前，这个内部引擎接口无法在 PHP 脚本中实现。必须改用 IteratorAggregate 或 Iterator。
While you cannot implement this interface, you can use it in your checks to determine if something is usable in for each. Here is what I use if I'm expecting something that must be iterable via foreach.
<?php
if( !is_array( $items ) && !$items instanceof Traversable )
//Throw exception here
?>NOTE: While objects and arrays can be traversed by foreach, they do NOT implement "Traversable", so you CANNOT check for foreach compatibility using an instanceof check.
Example:
$myarray = array('one', 'two', 'three');
$myobj = (object)$myarray;
if ( !($myarray instanceof \Traversable) ) {
print "myarray is NOT Traversable";
}
if ( !($myobj instanceof \Traversable) ) {
print "myobj is NOT Traversable";
}
foreach ($myarray as $value) {
print $value;
}
foreach ($myobj as $value) {
print $value;
}
Output:
myarray is NOT Traversable
myobj is NOT Traversable
one
two
three
one
two
threeThe PHP7 iterable pseudo type will match both Traversable and array. Great for return type-hinting so that you do not have to expose your Domain to Infrastructure code, e.g. instead of a Repository returning a Cursor, it can return hint 'iterable':
<?php
UserRepository::findUsers(): iterable
?>
Link: http://php.net/manual/en/migration71.new-features.php#migration71.new-features.iterable-pseudo-type
Also, instead of:
<?php
if( !is_array( $items ) && !$items instanceof Traversable )
//Throw exception here
?>
You can now do with the is_iterable() method:
<?php
if ( !is_iterable( $items ))
//Throw exception here
?>
Link: http://php.net/manual/en/function.is-iterable.phpNote that all objects can be iterated over with foreach anyway and it'll go over each property. This just describes whether or not the class implements an iterator, i.e. has custom behaviour.Actually you can use `Traversable` within your php scripts - you can use it to enforce iterability on user-land objects.
<?php
interface Stream implements \Traversable {}
class InMemoryStream implements IteratorAggregate, Stream
{
public function getIterator() {}
}
$stream = new InMemoryStream();
?>
In case you'd forgot about implementing `IteratorAggregate` or `Iterator` interfaces, fatal error will be raised when instantiating objects in question.
<?php
interface Stream implements \Traversable {}
class InMemoryStream implements Stream {}
$stream = new InMemoryStream(); // Fatal error: Class InMemoryStream must implement interface Traversable as part of either Iterator or IteratorAggregate in Unknown on line 0
?>