Hands on PHP 5.4: traits and other good stuff

Yesterday I had the opportunity to spend a few minutes on PHP 5.4 and its new features.

With David, we just set a Back|Track 4 VM on his Mac and downloaded the tar.gz of PHP 5.4 aplha 2.

To install it without running tests and loosing too much time:

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./configure
make && make install

So, ready to go!

Forget about multiple inheritance, enter reuse

A lot of people don’t like multiple inheritance because of the fact that a lot of stuff can be done doing proper OO design: nothing to say about that.

Although traits are also about multiple inheritance, their domain is more complex, as they usually deal with code reuse.

Consider, for example, this situation: from a Car we derive StandardCar and MiniCar, then we need to give cars a brand, which cannot be a simple attribute, because the brand deals with generating a car’s serial ID or – completely invented concept – deciding the minimum age the driver should have to drive it.

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<?php

class Car
{
  protected $manufacturer = NULL;

  public function getSerialId()
  {
    return rand(0, 999);
  }

  public function allowsDriversOver()
  {
    return 18;
  }
}

class StandardCar extends Car
{
}

class MiniCar extends Car
{
  public function allowsDriversOver()
  {
    return 16;
  }
}

So, let’s say BMW is the only vendor which does not follows a standard in generating serial IDs and does not let people under 21 to drive its cars: enter BmwCar and BmwMiniCar.

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<?php

class BmwCar extends StandardCar
{
  public function getSerialId()
  {
    return parent::getSerialId() . "-bmw";
  }

  // same for allowsDriversOver()
}

class BmwMiniCar extends MiniCar
{
  public function getSerialId()
  {
    return parent::getSerialId() . "-bmw";
  }

  // same for allowDriversOver()
}

This leads to duplications that we can avoid with traits:

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<?php

class BmwCar extends StandardCar
{
  use BmwManufactured;
}

class BmwMiniCar extends MiniCar
{
  use BmwManufactured;
}

trait BmwManufactured
{
  public function getSerialId()
  {
    return parent::getSerialId() . "-bmw";
  }
}

What I am personally missing is a is_with()/contains/whatsoever operator which checks if an object is an instance of a class implementing a certain trait, something like:

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<?php

$car->contains(BmwManufactured);

We looked for it, but could not find a solution: you can see that we introduced an ->isA($manufacturer) method in order to solve this. Completely inefficient logic: as far as I know this kind of operator will be implemented in the next releases of the PHP 5.4 development package, definitely a good thing.

Other good stuff

What a good thing the built-in webserver:

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php -S localhost:8124

which launches a webserver responding to the current directory: it will be really efficient when you are developing some standalone scripts in the need to be reached via HTTP.

I also – obviously – loved array deferencing:

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<?php

$a = array(
  'logger' => function () {
    echo 'loggin really serious stuff';
  }
);

$a['logger']() ;

which is awesome if you want to associatively store – for example – lambas in an array.

You can see the full list of our crappy PHP 5.4 experiments on this gist.