boot () 方法里的这些都是怎么回事，哪里来的？完全看不懂

<?php

namespace App\Providers;
use Gate;
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class AuthServiceProvider extends ServiceProvider
{
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public function boot()
{
$this->registerPolicies();
// 修改策略自动发现的逻辑
Gate::guessPolicyNamesUsing(function ($modelClass) {
// 动态返回模型对应的策略名称，如：// ‘App\Model\User’ => ‘App\Policies\UserPolicy’,
return ‘App\Policies\‘.class_basename($modelClass).’Policy’;
});
}
}