Traversable (遍历)接口

(PHP 5, PHP 7, PHP 8)

简介

检测一个类是否可以使用 foreach 进行遍历的接口。

无法被单独实现的基本抽象接口。相反,它必须由 IteratorAggregateIterator 接口实现。

接口摘要

interface Traversable {
}

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。

更新日志

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 IteratorIteratorAggregate

注释

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 IteratorAggregateIterator 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 IteratorAggregateIterator

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User Contributed Notes 5 notes

up
153
kevinpeno at gmail dot com
13 years ago
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
?>
up
83
cobaltbluedw
8 years ago
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
three
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51
douglas at reith dot com dot au
6 years ago
The 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.php
up
52
ajf at ajf dot me
9 years ago
Note 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.
up
-2
alan dot bem at gmail dot com
5 years ago
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
?>
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