Question

How to mimic C++ template classes in PHP?

EDITED1

For example how would this be in PHP?

template  <typename T>
class MyQueue
{
         std::vector<T> data;
      public:
         void Add(T const &d);
         void Remove();
         void Print();
};

Answer 1

Converting your C++ code to PHP:

class MyQueue{
  private $data;
  public function Add($d);
  public function Remove();
  public function Print();
};

As Thirler explained, PHP is dynamic, so you can pass anything you want to the Add function, and hold whatever values you want in $data. If you really wanted to add some type safety, you would have to pass the type you want to allow to the constructor.

public function __construct($t){
   $this->type = $t;
}

Then you can add some checks in other functions using the instanceof operator.

public function Add($d){
    if ( !($d instanceof $this->type ){
        throw new TypeException("The value passed to the function was not a {$this->type}");
    }
    //rest of the code here
}

However, it will not come close to the functionality of a statically typed languge that is designed to catch the type errors at compile time.