在另一个类的构造函数中实例化一个类

Question

I'd like to instantiate a class once, within another class' constructor, and then have access to it from all the functions of the class.

If you look at the following class, you can see that in function foo, I instantiate CLibrary and then call a function (callFn). This works fine.

What I would like to do is to instantiate CLibrary in the constructor (see comment) and then be able to use that variable ($library) in foo to access callFn (see the comments).

But this does not seem to work.

Can anybody help?

class CTweeting {
  private $library;
  private $ROOT;
  private $PHP_CLASSES;

  function __construct) {
        $this->ROOT        = $_SERVER['DOCUMENT_ROOT'];
    $this->PHP_CLASSES = $this->ROOT . "/php/classes/";
    require_once($this->PHP_CLASSES . 'CLibrary.php'); 
    //$library = new CLibrary(); // ** I would like to uncomment this line **



  public function foo() {
    $library = new CLibrary(); // …. delete this line
        $library->callFn();  // … and change this line to ‘$this->library->callFn();’
  }
}  

Answer 1

The $library variable can be used in your class constructor by doing $this->library

So the code should look like this:

class CTweeting { private $library; private $ROOT; private $PHP_CLASSES;

     function __construct) {
            $this->ROOT        = $_SERVER['DOCUMENT_ROOT'];
        $this->PHP_CLASSES = $this->ROOT . "/php/classes/";
        require_once($this->PHP_CLASSES . 'CLibrary.php'); 
        $this->library = new CLibrary(); 

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Answer 2

Here is a cleaned up version, using $this->library in the constructor and the foo() method

class CTweeting {
  private $library;
  private $ROOT;
  private $PHP_CLASSES;

  function __construct() {
     $this->ROOT        = $_SERVER['DOCUMENT_ROOT'];
     $this->PHP_CLASSES = $this->ROOT . "/php/classes/";
     require_once($this->PHP_CLASSES . 'CLibrary.php'); 
     $this->library = new CLibrary();
  }

  public function foo() {
     $this->library->callFn();
  }
}