在PHP依赖注入中，我是否需要“ require_once”定义依赖的php文件？

Question

Taking Fabien Potencier's example :

class User
{
  function __construct($storage)
  {
    $this->storage = $storage;
  }

  // ...
}

Assuming the Storage class is defined in a different php file (say, storage.php), do I need to include it in this file where the injection is done via a require_once?

Thanks,

JDelage

Answer 1

You should be putting all your require s and include s at the head of the file - that certainly a style thing, but for one thing it allows you to see by glancing at the source, what other files are need by your PHP file.

There are two cases:

1. You will only ever use user.php and storage.php from other files ( app.php say)
2. There are cases where you will use user.php and don't want to worry about remembering to require storage.php .

For #1 - you don't need to worry about requires, however there's no significant disadvantage to using require_once at the head of your PHP even if most of the time it'll have already been required.

For #2 - you need to use require_once at the header since you cannot use user.php without storage.php and the final page only knows it needs user.php .

short answer: Use require_once to include all dependencies for the code (to allow it to easily be used by other code)

note: You should only include direct-dependencies for the code. That is: if you have group.php that uses user.php , it should require_once 'user.php' , but need not worry about storage.php since it isn't directly used, and user.php implicitly includes it (that being said - no significant performance disadvantage of being thorough if you wish)