由于本人在学习laravel框架，在框架里面发现了很多的匿名函数，由于本来对这个没有了解，所以理解不了对应的框架逻辑。
然后，上网找了一些资料，最好的是这个个人觉得很好的 PHP Anonymous Functions 。大家可以过去看下，然后针对laravel的例子说一个：
步骤1. 在bootstrap/app.php目录下会有服务容器的绑定：
$app->singleton( Illuminate\Contracts\Http\Kernel::class, App\Http\Kernel::class );
$app->singleton( Illuminate\Contracts\Console\Kernel::class, App\Console\Kernel::class );
$app->singleton( Illuminate\Contracts\Debug\ExceptionHandler::class, App\Exceptions\Handler::class );
步骤2. 这里的singleton调用的是vendor/laravel/framework/src/Illuminate/Container/Container.php下的方法：
public function singleton($abstract, $concrete = null)
{
$this->bind($abstract, $concrete, true);
}
public function bind($abstract, $concrete = null, $shared = false)
{
// If no concrete type was given, we will simply set the concrete type to the
// abstract type. After that, the concrete type to be registered as shared
// without being forced to state their classes in both of the parameters.
$this->dropStaleInstances($abstract);
if (is_null($concrete)) {
$concrete = $abstract;
}
// If the factory is not a Closure, it means it is just a class name which is
// bound into this container to the abstract type and we will just wrap it
// up inside its own Closure to give us more convenience when extending.
if (! $concrete instanceof Closure) {
$concrete = $this->getClosure($abstract, $concrete);
}
$this->bindings[$abstract] = compact('concrete', 'shared');
// If the abstract type was already resolved in this container we'll fire the
// rebound listener so that any objects which have already gotten resolved
// can have their copy of the object updated via the listener callbacks.
if ($this->resolved($abstract)) {
$this->rebound($abstract);
}
}
步骤3. 上方的黑体斜体对应的就是下方的匿名方法：
protected function getClosure($abstract, $concrete)
{
return function ($container, $parameters = []) use ($abstract, $concrete) {
if ($abstract == $concrete) {
return $container->build($concrete);
}
return $container->make($concrete, $parameters);
};
}
步骤4. 这里会返回一个作为闭包的匿名函数用于处理服务容器的初始化，可是他这里的初始化还没有执行，这里只是绑定了这个服务容器方便后续调用。
步骤5. 最后会在public/index.php的初始化时调用：
$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);
步骤6. 上方调用的对应的是vendor/laravel/framework/src/Illuminate/Foundation/Application.php的make方法：
public function make($abstract, array $parameters = [])
{
$abstract = $this->getAlias($abstract);
if (isset($this->deferredServices[$abstract]) && ! isset($this->instances[$abstract])) {
$this->loadDeferredProvider($abstract);
}
return parent::make($abstract, $parameters);
}
步骤7. 这里会调用父类：vendor/laravel/framework/src/Illuminate/Container/Container.php的make方法
public function make($abstract, array $parameters = [])
{
return $this->resolve($abstract, $parameters);
}
protected function resolve($abstract, $parameters = [])
{
$abstract = $this->getAlias($abstract);
$needsContextualBuild = ! empty($parameters) || ! is_null(
$this->getContextualConcrete($abstract)
);
// If an instance of the type is currently being managed as a singleton we'll
// just return an existing instance instead of instantiating new instances
// so the developer can keep using the same objects instance every time.
if (isset($this->instances[$abstract]) && ! $needsContextualBuild) {
return $this->instances[$abstract];
}
$this->with[] = $parameters;
$concrete = $this->getConcrete($abstract);
// We're ready to instantiate an instance of the concrete type registered for
// the binding. This will instantiate the types, as well as resolve any of
// its "nested" dependencies recursively until all have gotten resolved.
if ($this->isBuildable($concrete, $abstract)) {
$object = $this->build($concrete);
} else {
$object = $this->make($concrete);
}
// If we defined any extenders for this type, we'll need to spin through them
// and apply them to the object being built. This allows for the extension
// of services, such as changing configuration or decorating the object.
foreach ($this->getExtenders($abstract) as $extender) {
$object = $extender($object, $this);
}
// If the requested type is registered as a singleton we'll want to cache off
// the instances in "memory" so we can return it later without creating an
// entirely new instance of an object on each subsequent request for it.
if ($this->isShared($abstract) && ! $needsContextualBuild) {
$this->instances[$abstract] = $object;
}
$this->fireResolvingCallbacks($abstract, $object);
// Before returning, we will also set the resolved flag to "true" and pop off
// the parameter overrides for this build. After those two things are done
// we will be ready to return back the fully constructed class instance.
$this->resolved[$abstract] = true;
array_pop($this->with);
return $object;
}
步骤8. 因为第一次是初始化，所以调用了container的build方法：
public function build($concrete)
{
// If the concrete type is actually a Closure, we will just execute it and
// hand back the results of the functions, which allows functions to be
// used as resolvers for more fine-tuned resolution of these objects.
if ($concrete instanceof Closure) {
return $concrete($this, $this->getLastParameterOverride());
}
$reflector = new ReflectionClass($concrete);
// If the type is not instantiable, the developer is attempting to resolve
// an abstract type such as an Interface of Abstract Class and there is
// no binding registered for the abstractions so we need to bail out.
if (! $reflector->isInstantiable()) {
return $this->notInstantiable($concrete);
}
$this->buildStack[] = $concrete;
$constructor = $reflector->getConstructor();
// If there are no constructors, that means there are no dependencies then
// we can just resolve the instances of the objects right away, without
// resolving any other types or dependencies out of these containers.
if (is_null($constructor)) {
array_pop($this->buildStack);
return new $concrete;
}
$dependencies = $constructor->getParameters();
// Once we have all the constructor's parameters we can create each of the
// dependency instances and then use the reflection instances to make a
// new instance of this class, injecting the created dependencies in.
$instances = $this->resolveDependencies(
$dependencies
);
array_pop($this->buildStack);
return $reflector->newInstanceArgs($instances);
}
步骤9. 上方的 $concrete 为步骤３处返回的那个匿名函数，这里的$concrete($this, $this->getLastParameterOverride());相当于调用了步骤３的方法： function($container, $parameters = []) use ($abstract, $concrete)
调用方法的参数一一对应：
$this ----------- $containser
$this->getLastParameterOverride() --------------------- $parameters
$abstract, $concrete这两个的话对应回原来调用时的数据
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