管道的一般逻辑
- 可以动态的添加管道处理命令
- 传入初始的数据，依次经过管道处理
- 满足一定条件跳出管道，否则经由下一个管道命令处理
简单实现
function pipeA($in) {
if ($condition) {
return 'break';
}
return do_something($in);
}
// function pipeB
// function pipeC
$pipes = ['pipeA', 'pipeB', 'pipeC'];
$data = 'before pipe';
foreach ($pipes as $pipe) {
$data = $pipe($data);
if ($condition_break) {
break;
}
}
printf("after pipe: %s", $data);
代码看起来没啥问题，除了一点小瑕疵。我们注意到pipeA函数里始终需要有一个返回标识来告诉Pipe什么时候需要进入下一个管道命令，什么时候需要跳出。我们可以改进一下：
function pipeA($in) {
if ($condition) {
return ['break', 'return value'];
}
return ['continue', 'prepare to next'];
}
// function pipeB
// function pipeC
$pipes = ['pipeA', 'pipeB', 'pipeC'];
$data = 'before pipe';
foreach ($pipes as $pipe) {
list($flag, $data) = $pipe($data);
if ($flag == 'break') {
break;
}
}
printf("after pipe: %s", $data);
这次看起来问题得到了解决，然而在工程上很容易产生问题：管道函数会由不同的开发人员定义，他们可能不能严格遵循上面这种苛刻的返回结果。我们希望有一种更简单明确的管道写法，满足条件则返回，否则进入下一个管道。例如传入闭包就很不错：
function pipe($data, $next) {
if ($condition) {
return $result;
} else {
// process by next pipe
return $next($data);
}
}
可是这样一来，我们的管道处理过程应该怎么写呢？我们发现，这个$next闭包，实际上嵌套包含了后面所有的管道处理函数：
pipeA()
else $nextA()
$nextA = function(){
pipeB()
else $nextB()
};
$nextB = function() {
pipeC()
else $nextC()
}
...
也就是说，我们需要从最后一个管道命令开始嵌套定义这个闭包，然后再执行闭包函数：
function pipeA($in, $next) {
if (!random_int(0, 3)) {
return $in . ' break in pipe A';
}
return $next($in.' through A');
}
function pipeB($in, $next) {
if (!random_int(0, 2)) {
return $in . ' break in pipe B';
}
return $next($in.' through B');
}
function pipeC($in, $next) {
if (!random_int(0, 1)) {
return $in . ' break in pipe C';
}
return $next($in.' through C');
}
$pipes = ['pipeA', 'pipeB', 'pipeC'];
$data = 'Dapianzi';
// 创建闭包
function create_next($next, $curr) {
// 返回一个闭包，接收待处理的管道数据
return function($data) use ($next, $curr) {
// 将待处理的数据和下一个管道命令传入当前管道命令
return $curr($data, $next);
};
}
// 初始闭包 $next
// 实际上最后执行
$next = function($data) {
return $data . ' pipe done';
};
// 从尾巴开始定义闭包$next
$pipes = array_reverse($pipes);
foreach ($pipes as $pipe) {
$next = create_next($next, $pipe);
}
$data = $next($data);
printf("after pipe: %s", $data);
我们有一个初始化的$next, 依次访问$pipes数组的每个元素，最后返回一个$next。如果你有印象的话，马上就会想到这不就是array_reduce吗？
// function pipeA, pipeB, pipeC
$pipes = ['pipeA', 'pipeB', 'pipeC'];
$data = 'Dapianzi';
$pipeline = array_reduce(array_reverse($pipes), function($next, $curr) {
return function($data) use ($next, $curr) {
return $curr($data, $next);
};
}, function($data) {
return $data . ' pipe done';
});
$data = $pipeline($data);
printf("after pipe: %s", $data);
至此，一个简单的Pipeline就完成了。
比较Pipeline源码
最后贴一个Laravel中对Pipeline实现的源码，跟上面不能说大同小异吧，简直就是一摸一样（确信）。
<?php
namespace Illuminate\Pipeline;
use Closure;
use Illuminate\Contracts\Container\Container;
use Illuminate\Contracts\Pipeline\Pipeline as PipelineContract;
use RuntimeException;
use Throwable;
class Pipeline implements PipelineContract
{
/**
* The container implementation.
*
* @var \Illuminate\Contracts\Container\Container
*/
protected $container;
/**
* The object being passed through the pipeline.
*
* @var mixed
*/
protected $passable;
/**
* The array of class pipes.
*
* @var array
*/
protected $pipes = [];
/**
* The method to call on each pipe.
*
* @var string
*/
protected $method = 'handle';
/**
* Create a new class instance.
*
* @param \Illuminate\Contracts\Container\Container|null $container
* @return void
*/
public function __construct(Container $container = null)
{
$this->container = $container;
}
/**
* Set the object being sent through the pipeline.
*
* @param mixed $passable
* @return $this
*/
public function send($passable)
{
$this->passable = $passable;
return $this;
}
/**
* Set the array of pipes.
*
* @param array|mixed $pipes
* @return $this
*/
public function through($pipes)
{
$this->pipes = is_array($pipes) ? $pipes : func_get_args();
return $this;
}
/**
* Set the method to call on the pipes.
*
* @param string $method
* @return $this
*/
public function via($method)
{
$this->method = $method;
return $this;
}
/**
* Run the pipeline with a final destination callback.
*
* @param \Closure $destination
* @return mixed
*/
public function then(Closure $destination)
{
$pipeline = array_reduce(
array_reverse($this->pipes()), $this->carry(), $this->prepareDestination($destination)
);
return $pipeline($this->passable);
}
/**
* Run the pipeline and return the result.
*
* @return mixed
*/
public function thenReturn()
{
return $this->then(function ($passable) {
return $passable;
});
}
/**
* Get the final piece of the Closure onion.
*
* @param \Closure $destination
* @return \Closure
*/
protected function prepareDestination(Closure $destination)
{
return function ($passable) use ($destination) {
try {
return $destination($passable);
} catch (Throwable $e) {
return $this->handleException($passable, $e);
}
};
}
/**
* Get a Closure that represents a slice of the application onion.
*
* @return \Closure
*/
protected function carry()
{
return function ($stack, $pipe) {
return function ($passable) use ($stack, $pipe) {
try {
if (is_callable($pipe)) {
// If the pipe is a callable, then we will call it directly, but otherwise we
// will resolve the pipes out of the dependency container and call it with
// the appropriate method and arguments, returning the results back out.
return $pipe($passable, $stack);
} elseif (! is_object($pipe)) {
[$name, $parameters] = $this->parsePipeString($pipe);
// If the pipe is a string we will parse the string and resolve the class out
// of the dependency injection container. We can then build a callable and
// execute the pipe function giving in the parameters that are required.
$pipe = $this->getContainer()->make($name);
$parameters = array_merge([$passable, $stack], $parameters);
} else {
// If the pipe is already an object we'll just make a callable and pass it to
// the pipe as-is. There is no need to do any extra parsing and formatting
// since the object we're given was already a fully instantiated object.
$parameters = [$passable, $stack];
}
$carry = method_exists($pipe, $this->method)
? $pipe->{$this->method}(...$parameters)
: $pipe(...$parameters);
return $this->handleCarry($carry);
} catch (Throwable $e) {
return $this->handleException($passable, $e);
}
};
};
}
/**
* Parse full pipe string to get name and parameters.
*
* @param string $pipe
* @return array
*/
protected function parsePipeString($pipe)
{
[$name, $parameters] = array_pad(explode(':', $pipe, 2), 2, []);
if (is_string($parameters)) {
$parameters = explode(',', $parameters);
}
return [$name, $parameters];
}
/**
* Get the array of configured pipes.
*
* @return array
*/
protected function pipes()
{
return $this->pipes;
}
/**
* Get the container instance.
*
* @return \Illuminate\Contracts\Container\Container
*
* @throws \RuntimeException
*/
protected function getContainer()
{
if (! $this->container) {
throw new RuntimeException('A container instance has not been passed to the Pipeline.');
}
return $this->container;
}
/**
* Set the container instance.
*
* @param \Illuminate\Contracts\Container\Container $container
* @return $this
*/
public function setContainer(Container $container)
{
$this->container = $container;
return $this;
}
/**
* Handle the value returned from each pipe before passing it to the next.
*
* @param mixed $carry
* @return mixed
*/
protected function handleCarry($carry)
{
return $carry;
}
/**
* Handle the given exception.
*
* @param mixed $passable
* @param \Throwable $e
* @return mixed
*
* @throws \Throwable
*/
protected function handleException($passable, Throwable $e)
{
throw $e;
}
}