淺析PHP類的反射來(lái)實(shí)現(xiàn)依賴注入過(guò)程

/**
 * Class Point
 */
class Point
{
  public $x;
  public $y;

  /**
   * Point constructor.
   * @param int $x horizontal value of point's coordinate
   * @param int $y vertical value of point's coordinate
   */
  public function __construct($x = 0, $y = 0)
  {
    $this->x = $x;
    $this->y = $y;
  }
}

class Circle
{
  /**
   * @var int
   */
  public $radius;//半徑

  /**
   * @var Point
   */
  public $center;//圓心點(diǎn)

  const PI = 3.14;

  public function __construct(Point $point, $radius = 1)
  {
    $this->center = $point;
    $this->radius = $radius;
  }
  
  //打印圓點(diǎn)的坐標(biāo)
  public function printCenter()
  {
    printf('center coordinate is (%d, %d)', $this->center->x, $this->center->y);
  }

  //計(jì)算圓形的面積
  public function area()
  {
    return 3.14 * pow($this->radius, 2);
  }
}

$reflectionClass = new reflectionClass(Circle::class);
//返回值如下
object(ReflectionClass)#1 (1) {
 ["name"]=>
 string(6) "Circle"
}

$reflectionClass->getConstants();

array(1) {
 ["PI"]=>
 float(3.14)
}

$reflectionClass->getProperties();

array(2) {
 [0]=>
 object(ReflectionProperty)#2 (2) {
  ["name"]=>
  string(6) "radius"
  ["class"]=>
  string(6) "Circle"
 }
 [1]=>
 object(ReflectionProperty)#3 (2) {
  ["name"]=>
  string(6) "center"
  ["class"]=>
  string(6) "Circle"
 }
}

$reflectionClass->getMethods();

array(3) {
 [0]=>
 object(ReflectionMethod)#2 (2) {
  ["name"]=>
  string(11) "__construct"
  ["class"]=>
  string(6) "Circle"
 }
 [1]=>
 object(ReflectionMethod)#3 (2) {
  ["name"]=>
  string(11) "printCenter"
  ["class"]=>
  string(6) "Circle"
 }
 [2]=>
 object(ReflectionMethod)#4 (2) {
  ["name"]=>
  string(4) "area"
  ["class"]=>
  string(6) "Circle"
 }
}

$constructor = $reflectionClass->getConstructor();

$parameters = $constructor->getParameters();

array(2) {
 [0]=>
 object(ReflectionParameter)#3 (1) {
  ["name"]=>
  string(5) "point"
 }
 [1]=>
 object(ReflectionParameter)#4 (1) {
  ["name"]=>
  string(6) "radius"
 }
}

//構(gòu)建類的對(duì)象
function make($className)
{
  $reflectionClass = new ReflectionClass($className);
  $constructor = $reflectionClass->getConstructor();
  $parameters = $constructor->getParameters();
  $dependencies = getDependencies($parameters);
  
  return $reflectionClass->newInstanceArgs($dependencies);
}

//依賴解析
function getDependencies($parameters)
{
  $dependencies = [];
  foreach($parameters as $parameter) {
    $dependency = $parameter->getClass();
    if (is_null($dependency)) {
      if($parameter->isDefaultValueAvailable()) {
        $dependencies[] = $parameter->getDefaultValue();
      } else {
        //不是可選參數(shù)的為了簡(jiǎn)單直接賦值為字符串0
        //針對(duì)構(gòu)造方法的必須參數(shù)這個(gè)情況
        //laravel是通過(guò)service provider注冊(cè)closure到IocContainer,
        //在closure里可以通過(guò)return new Class($param1, $param2)來(lái)返回類的實(shí)例
        //然后在make時(shí)回調(diào)這個(gè)closure即可解析出對(duì)象
        //具體細(xì)節(jié)我會(huì)在另一篇文章里面描述
        $dependencies[] = '0';
      }
    } else {
      //遞歸解析出依賴類的對(duì)象
      $dependencies[] = make($parameter->getClass()->name);
    }
  }

  return $dependencies;
}

$circle = make('Circle');
$area = $circle->area();
/*var_dump($circle, $area);
object(Circle)#6 (2) {
 ["radius"]=>
 int(1)
 ["center"]=>
 object(Point)#11 (2) {
  ["x"]=>
  int(0)
  ["y"]=>
  int(0)
 }
}
float(3.14)*/