RecursiveIteratorIterator如何在PHP中工作？ [英] How does RecursiveIteratorIterator work in PHP?
问题描述
RecursiveIteratorIterator 是如何工作的？
PHP手册没有太多记录或解释。 IteratorIterator 和 RecursiveIteratorIterator 之间有什么区别？
RecursiveIteratorIterator 是一个具体的 ：//php.net/Traversablerel =noreferrer> Traversable 允许 foreach 迭代： $ path ='tree';
$ dir = new DirectoryIterator（$ path）;
echo[$ path] \ n;
foreach（$ dir as $ file）{
echo├$ file\\\
;
}
上面目录结构的示例输出是：
[tree] $ b $b├。 $ b $b├.. $ b $b├dirA$ b $b├文件A
当你看到这还没有使用 IteratorIterator 或 RecursiveIteratorIterator 。相反，它只是使用 foreach 在 Traversable 界面上运行。
As foreach 默认只知道名为线性顺序的迭代类型，我们可能希望明确指定迭代类型。乍一看它看起来似乎太冗长了，但为了演示目的（并且为了与 RecursiveIteratorIterator 稍后更加明显），让我们指定显式指定<的迭代的线性类型code> IteratorIterator 目录列表的迭代类型：
$ files = new IteratorIterator （$ DIR）;
echo[$ path] \ n;
foreach（$ files as $ file）{
echo├$ file\\\
;
}
这个例子几乎与第一个相同，区别在于 $ files 现在是迭代的 Traversable的 IteratorIterator 类型 $ dir ：
$ files = new IteratorIterator （$ DIR）;
像往常一样，迭代行为由 foreach ：
foreach（$ files as $ file）{
输出完全相同。那有什么不同呢？不同的是 foreach 中使用的对象。在第一个示例中，它是 DirectoryIterator ，在第二个示例中，它是 IteratorIterator 。这显示了迭代器的灵活性：你可以互相替换它们， foreach 里面的代码只是继续按预期工作。
让我们开始获取整个列表，包括子目录。
我们现在已经指定了迭代的类型，让我们考虑将其更改为另一种迭代类型。
我们知道我们现在需要遍历整个树，而不仅仅是第一层。要使用简单的 foreach ，我们需要一种不同类型的迭代器： RecursiveIteratorIterator 。并且只能迭代具有 RecursiveIterator 界面的容器对象。
接口是合约。任何实现它的类都可以与 RecursiveIteratorIterator 一起使用。这样一个类的一个例子是 RecursiveDirectoryIterator ，这是类似于 DirectoryIterator 的递归变体。
让我们在用I编写任何其他句子之前看第一个代码示例-word：
$ dir = new RecursiveDirectoryIterator（$ path）;
echo[$ path] \ n;
foreach（$ dir as $ file）{
echo├$ file\\\
;
}
第三个例子几乎与第一个相同一，但它创造了一些不同的输出：
[tree] $ b $b├tree\。 $ b $b├tree\ .. $ b $b├tree\dirA $ b $b├chree\fileA
好的，没有那么不同，文件名现在包含前面的路径名，但其余的看起来也相似。
如示例所示，即使目录对象已经嵌入 RecursiveIterator 接口，这还不足以使 foreach 遍历整个目录树。这是 RecursiveIteratorIterator 开始运作的地方。 示例4 显示了如何：
$ files = new RecursiveIteratorIterator（$ dir）;
echo[$ path] \ n;
foreach（$ files as $ file）{
echo├$ file\\\
;
}
使用 RecursiveIteratorIterator 而不是只是前面的 $ dir 对象将使 foreach 以递归方式遍历所有文件和目录。然后列出所有文件，因为现在已经指定了对象迭代的类型：
[tree] $ b $b├树\。 $ b $b├tree\ .. $ b $b├tree\dirA\。 $ b $b├tree\dirA\ .. $ b $b├tree\dirA\dirB\。 $ b $b├tree\dirA\dirB\ .. $ b $b├tree\dirA\dirB\fileD $ b $b├tree\dirA\fileB $ b $b├tree \\ dirA\fileC $ b $b├chree\fileA
这应该已经证明了它们之间的区别平面和树遍历。 RecursiveIteratorIterator 能够将任何树状结构遍历为元素列表。因为有更多的信息（比如迭代当前所处的级别），所以可以在迭代它时访问迭代器对象，例如缩进输出：
echo[$ path] \ n;
foreach（$ files as $ file）{
$ indent = str_repeat（''，$ files-> getDepth（））;
echo $ indent，├$ file \ n;
}
示例5的输出：
[tree] $ b $b├three\。 $ b $b├tree\ .. $ b $b├tree\dirA\。 $ b $b├tree\dirA\ .. $ b $b├tree\dirA\dirB\。 $ b $b├tree\dirA\dirB\ .. $ b $b├tree\dirA\dirB\fileD $ b $b├tree\dirA\fileB $ b $b├tree \\ dirA\fileC $ b $b├chree\fileA
当然这不会赢得美女竞争，但它表明，使用递归迭代器可以获得更多信息，而不仅仅是 key 和 value 的线性顺序。即使 foreach 也只能表达这种线性，访问迭代器本身就可以获得更多信息。
类似于元信息还有不同的方法如何遍历树并因此排序输出。这是的 模式 RecursiveIteratorIterator ，可以使用构造函数设置它。
下一个示例将告诉 RecursiveDirectoryIterator 删除点条目（。和 .. ），因为我们不需要它们。但是，递归模式也将更改为在子项（子目录中的文件和子子目录）之前首先获取父元素（子目录）（ SELF_FIRST ）： / p>
$ dir = new RecursiveDirectoryIterator（$ path，RecursiveDirectoryIterator :: SKIP_DOTS）;
$ files = new RecursiveIteratorIterator（$ dir，RecursiveIteratorIterator :: SELF_FIRST）;
echo[$ path] \ n;
foreach（$ files as $ file）{
$ indent = str_repeat（''，$ files-> getDepth（））;
echo $ indent，├$ file \ n;
}
输出现在显示正确列出的子目录条目，如果你与前一个相比较那些不在那里的输出：
[tree] $ b $b├tree\dirA $ b $b├tree\ dirA\dirB $ b $b├tree\dirA\dirB\fileD $ b $b├tree\dirA\fileB $ b $b├tree\dirA\fileC $ b $b├tree \\ fileA
因此，递归模式控制返回树中brach或leaf的内容和时间，目录示例：
-
LEAVES_ONLY（默认）：仅列出文件，没有目录。 -
SELF_FIRST（上图）：列出目录，然后是那里的文件。 -
CHILD_FIRST（没有示例）：首先列出子目录中的文件，然后列出目录。
使用其他两种模式输出示例5 ：
LEAVES_ONLY CHILD_FIRST
[树] [树] $ b $b├tree\dirA\dirB\fileD├tree\dirA\dirB\fileD $ b $b├tree\dirA \fileB├tree\dirA \dirB $ b $b├tree\dirA\fileC├sree\dirA\fileB $ b $b├tree\fileA├tree\dirA\fileC $ b $b├tree \dirA $ b $b├tree\fileA
当你将它与标准遍历，所有这些东西都不可用。因此，当你需要绕过它时，递归迭代会稍微复杂一点，但它很容易使用，因为它的行为就像迭代器一样，你将它放入 foreach 并完成。
我认为这些是一个答案的足够例子。您可以在此要点中找到完整的源代码以及显示漂亮的ascii-trees的示例： https： //gist.github.com/3599532
自己动手：制作
RecursiveTreeIterator逐行工作。
示例5 演示了有关迭代器可用状态的元信息。但是，这是在 foreach 迭代中有目的地演示。在现实生活中，这自然属于 RecursiveIterator 。
更好的例子是 RecursiveTreeIterator ，它负责缩进，前缀等。请参阅以下代码片段：
$ dir = new RecursiveDirectoryIterator（$ path，RecursiveDirectoryIterator :: SKIP_DOTS）;
$ lines = new RecursiveTreeIterator（$ dir）;
$ unicodeTreePrefix（$ lines）;
echo[$ path] \ n，implode（\ n，iterator_to_array（$ lines））;
RecursiveTreeIterator 旨在通过以下方式工作：线，输出非常直接，有一个小问题：
[tree] $ b $b├tree\dirA $ b $b│├tree \dirA\dirB $ b $b││└sreeh\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\ dirA\fileC $ b $b└chree\fileA
与<组合使用时code> RecursiveDirectoryIterator 它显示整个路径名，而不仅仅是文件名。其余的看起来不错。这是因为文件名是由 SplFileInfo 生成的。这些应该显示为基本名称。所需的输出如下：
///已解决///
[tree] $ b $b├dirA$ b $b│├dirB$ b $b││└fileD$ b $b│├文件B $ b $b│└cileC$ b $b└fileA
创建一个可与 RecursiveTreeIterator 一起使用的装饰器类，而不是 RecursiveDirectoryIterator 。它应该提供当前 SplFileInfo 的基本名称，而不是路径名。最终的代码片段可能如下所示：
$ lines = new RecursiveTreeIterator（
new DiyRecursiveDecorator（$ dir）
）;
$ unicodeTreePrefix（$ lines）;
echo[$ path] \ n，implode（\ n，iterator_to_array（$ lines））;
这些片段包括 $ unicodeTreePrefix 属于附录中的要点：自己动手：制作 RecursiveTreeIterator 逐行工作。。
How does RecursiveIteratorIterator work?
The PHP manual has nothing much documented or explained. What is the difference between IteratorIterator and RecursiveIteratorIterator?
RecursiveIteratorIterator is a concrete Iterator implementing tree traversal. It enables a programmer to traverse a container object that implements the RecursiveIterator interface, see Iterator in Wikipedia for the general principles, types, semantics and patterns of iterators.
In difference to IteratorIterator which is a concrete Iterator implementing object traversal in linear order (and by default accepting any kind of Traversable in its constructor), the RecursiveIteratorIterator allows looping over all nodes in an ordered tree of objects and its constructor takes a RecursiveIterator.
In short: RecursiveIteratorIterator allows you to loop over a tree, IteratorIterator allows you to loop over a list. I show that with some code examples below soon.
Technically this works by breaking out of linearity by traversing all of a nodes' children (if any). This is possible because by definition all children of a node are again a RecursiveIterator. The toplevel Iterator then internally stacks the different RecursiveIterators by their depth and keeps a pointer to the current active sub Iterator for traversal.
This allows to visit all nodes of a tree.
The underlying principles are the same as with IteratorIterator: An interface specifies the type of iteration and the base iterator class is the implementation of these semantics. Compare with the examples below, for linear looping with foreach you normally do not think about the implementation details much unless you need to define a new Iterator (e.g. when some concrete type itself does not implement Traversable).
For recursive traversal - unless you do not use a pre-defined Traversal that already has recursive traversal iteration - you normally need to instantiate the existing RecursiveIteratorIterator iteration or even write a recursive traversal iteration that is a Traversable your own to have this type of traversal iteration with foreach.
Tip: You probably didn't implement the one nor the other your own, so this might be something worth to do for your practical experience of the differences they have. You find a DIY suggestion at the end of the answer.
Technical differences in short:
- While
IteratorIteratortakes anyTraversablefor linear traversal,RecursiveIteratorIteratorneeds a more specificRecursiveIteratorto loop over a tree. - Where
IteratorIteratorexposes its mainIteratorviagetInnerIerator(),RecursiveIteratorIteratorprovides the current active sub-Iteratoronly via that method. - While
IteratorIteratoris totally not aware of anything like parent or children,RecursiveIteratorIteratorknows how to get and traverse children as well. IteratorIteratordoes not need a stack of iterators,RecursiveIteratorIteratorhas such a stack and knows the active sub-iterator.- Where
IteratorIteratorhas its order due to linearity and no choice,RecursiveIteratorIteratorhas a choice for further traversal and needs to decide per each node (decided via mode perRecursiveIteratorIterator). RecursiveIteratorIteratorhas more methods thanIteratorIterator.
To summarize: RecursiveIterator is a concrete type of iteration (looping over a tree) that works on its own iterators, namely RecursiveIterator. That is the same underlying principle as with IteratorIerator, but the type of iteration is different (linear order).
Ideally you can create your own set, too. The only thing necessary is that your iterator implements Traversable which is possible via Iterator or IteratorAggregate. Then you can use it with foreach. For example some kind of ternary tree traversal recursive iteration object together with the according iteration interface for the container object(s).
Let's review with some real-life examples that are not that abstract. Between interfaces, concrete iterators, container objects and iteration semantics this maybe is not a that bad idea.
Take a directory listing as an example. Consider you have got the following file and directory tree on disk:
While a iterator with linear order just traverse over the toplevel folder and files (a single directory listing), the recursive iterator traverses through subfolders as well and list all folders and files (a directory listing with listings of its subdirectories):
Non-Recursive Recursive
============= =========
[tree] [tree]
├ dirA ├ dirA
└ fileA │ ├ dirB
│ │ └ fileD
│ ├ fileB
│ └ fileC
└ fileA
You can easily compare this with IteratorIterator which does no recursion for traversing the directory tree. And the RecursiveIteratorIterator which can traverse into the tree as the Recursive listing shows.
At first a very basic example with a DirectoryIterator that implements Traversable which allows foreach to iterate over it:
$path = 'tree';
$dir = new DirectoryIterator($path);
echo "[$path]\n";
foreach ($dir as $file) {
echo " ├ $file\n";
}
The exemplary output for the directory structure above then is:
[tree]
├ .
├ ..
├ dirA
├ fileA
As you see this is not yet using IteratorIterator or RecursiveIteratorIterator. Instead it just just using foreach that operates on the Traversable interface.
As foreach by default only knows the type of iteration named linear order, we might want to specify the type of iteration explicitly. At first glance it might seem too verbose, but for demonstration purposes (and to make the difference with RecursiveIteratorIterator more visible later), lets specify the linear type of iteration explicitly specifying the IteratorIterator type of iteration for the directory listing:
$files = new IteratorIterator($dir);
echo "[$path]\n";
foreach ($files as $file) {
echo " ├ $file\n";
}
This example is nearly identical with the first one, the difference is that $files is now an IteratorIterator type of iteration for Traversable $dir:
$files = new IteratorIterator($dir);
As usual the act of iteration is performed by the foreach:
foreach ($files as $file) {
The output is exactly the same. So what is different? Different is the object used within the foreach. In the first example it is a DirectoryIterator in the second example it is the IteratorIterator. This shows the flexibility iterators have: You can replace them with each other, the code inside foreach just continue to work as expected.
Lets start to get the whole listing, including subdirectories.
As we now have specified the type of iteration, let's consider to change it to another type of iteration.
We know we need to traverse the whole tree now, not only the first level. To have that work with a simple foreach we need a different type of iterator: RecursiveIteratorIterator. And that one can only iterate over container objects that have the RecursiveIterator interface.
The interface is a contract. Any class implementing it can be used together with the RecursiveIteratorIterator. An example of such a class is the RecursiveDirectoryIterator, which is something like the recursive variant of DirectoryIterator.
Lets see a first code example before writing any other sentence with the I-word:
$dir = new RecursiveDirectoryIterator($path);
echo "[$path]\n";
foreach ($dir as $file) {
echo " ├ $file\n";
}
This third example is nearly identical with the first one, however it creates some different output:
[tree]
├ tree\.
├ tree\..
├ tree\dirA
├ tree\fileA
Okay, not that different, the filename now contains the pathname in front, but the rest looks similar as well.
As the example shows, even the directory object already imlements the RecursiveIterator interface, this is not yet enough to make foreach traverse the whole directory tree. This is where the RecursiveIteratorIterator comes into action. Example 4 shows how:
$files = new RecursiveIteratorIterator($dir);
echo "[$path]\n";
foreach ($files as $file) {
echo " ├ $file\n";
}
Using the RecursiveIteratorIterator instead of just the previous $dir object will make foreach to traverse over all files and directories in a recursive manner. This then lists all files, as the type of object iteration has been specified now:
[tree]
├ tree\.
├ tree\..
├ tree\dirA\.
├ tree\dirA\..
├ tree\dirA\dirB\.
├ tree\dirA\dirB\..
├ tree\dirA\dirB\fileD
├ tree\dirA\fileB
├ tree\dirA\fileC
├ tree\fileA
This should already demonstrate the difference between flat and tree traversal. The RecursiveIteratorIterator is able to traverse any tree-like structure as a list of elements. Because there is more information (like the level the iteration takes currently place), it is possible to access the iterator object while iterating over it and for example indent the output:
echo "[$path]\n";
foreach ($files as $file) {
$indent = str_repeat(' ', $files->getDepth());
echo $indent, " ├ $file\n";
}
And output of Example 5:
[tree]
├ tree\.
├ tree\..
├ tree\dirA\.
├ tree\dirA\..
├ tree\dirA\dirB\.
├ tree\dirA\dirB\..
├ tree\dirA\dirB\fileD
├ tree\dirA\fileB
├ tree\dirA\fileC
├ tree\fileA
Sure this does not win a beauty contest, but it shows that with the recursive iterator there is more information available than just the linear order of key and value. Even foreach can only express this kind of linearity, accessing the iterator itself allows to obtain more information.
Similar to the meta-information there are also different ways possible how to traverse the tree and therefore order the output. This is the Mode of the RecursiveIteratorIterator and it can be set with the constructor.
The next example will tell the RecursiveDirectoryIterator to remove the dot entries (. and ..) as we do not need them. But also the recursion mode will be changed to take the parent element (the subdirectory) first (SELF_FIRST) before the children (the files and sub-subdirs in the subdirectory):
$dir = new RecursiveDirectoryIterator($path, RecursiveDirectoryIterator::SKIP_DOTS);
$files = new RecursiveIteratorIterator($dir, RecursiveIteratorIterator::SELF_FIRST);
echo "[$path]\n";
foreach ($files as $file) {
$indent = str_repeat(' ', $files->getDepth());
echo $indent, " ├ $file\n";
}
The output now shows the subdirectory entries properly listed, if you compare with the previous output those were not there:
[tree]
├ tree\dirA
├ tree\dirA\dirB
├ tree\dirA\dirB\fileD
├ tree\dirA\fileB
├ tree\dirA\fileC
├ tree\fileA
The recursion mode therefore controls what and when a brach or leaf in the tree is returned, for the directory example:
LEAVES_ONLY(default): Only list files, no directories.SELF_FIRST(above): List directory and then the files in there.CHILD_FIRST(w/o example): List files in subdirectory first, then the directory.
Output of Example 5 with the two other modes:
LEAVES_ONLY CHILD_FIRST
[tree] [tree]
├ tree\dirA\dirB\fileD ├ tree\dirA\dirB\fileD
├ tree\dirA\fileB ├ tree\dirA\dirB
├ tree\dirA\fileC ├ tree\dirA\fileB
├ tree\fileA ├ tree\dirA\fileC
├ tree\dirA
├ tree\fileA
When you compare that with standard traversal, all these things are not available. Recursive iteration therefore is a little bit more complex when you need to wrap your head around it, however it is easy to use because it behaves just like an iterator, you put it into a foreach and done.
I think these are enough examples for one answer. You can find the full source-code as well as an example to display nice-looking ascii-trees in this gist: https://gist.github.com/3599532
Do It Yourself: Make the
RecursiveTreeIteratorWork Line by Line.
Example 5 demonstrated that there is meta-information about the iterator's state available. However, this was purposefully demonstrated within the foreach iteration. In real life this naturally belongs inside the RecursiveIterator.
A better example is the RecursiveTreeIterator, it takes care of indenting, prefixing and so on. See the following code fragment:
$dir = new RecursiveDirectoryIterator($path, RecursiveDirectoryIterator::SKIP_DOTS);
$lines = new RecursiveTreeIterator($dir);
$unicodeTreePrefix($lines);
echo "[$path]\n", implode("\n", iterator_to_array($lines));
The RecursiveTreeIterator is intended to work line by line, the output is pretty straight forward with one little problem:
[tree]
├ tree\dirA
│ ├ tree\dirA\dirB
│ │ └ tree\dirA\dirB\fileD
│ ├ tree\dirA\fileB
│ └ tree\dirA\fileC
└ tree\fileA
When used in combination with a RecursiveDirectoryIterator it displays the whole pathname and not just the filename. The rest looks good. This is because the file-names are generated by SplFileInfo. Those should be displayed as the basename instead. The desired output is the following:
/// Solved ///
[tree]
├ dirA
│ ├ dirB
│ │ └ fileD
│ ├ fileB
│ └ fileC
└ fileA
Create a decorator class that can be used with RecursiveTreeIterator instead of the RecursiveDirectoryIterator. It should provide the basename of the current SplFileInfo instead of the pathname. The final code fragment could then look like:
$lines = new RecursiveTreeIterator(
new DiyRecursiveDecorator($dir)
);
$unicodeTreePrefix($lines);
echo "[$path]\n", implode("\n", iterator_to_array($lines));
These fragments including $unicodeTreePrefix are part of the gist in Appendix: Do It Yourself: Make the RecursiveTreeIterator Work Line by Line..
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