Lazy-loading for PHP

example.php

<?php

class Address {
  public $street;
  public $town;
}

class Customer {
  public $id;
  public $name;
  public $address;
}

class Payment {
  public $amount;
  public $customer;
}

$db = getDatabase();
$payment = $db->load('Payment', 123);
/*
$payment containts:
  amount = 100;
  customer = class Customer {
    id = 5;
    name = uninitialized;
    address = uninitialized;
  }
}
*/

echo $payment->customer->name; // DB layer will load customer info

// or 
echo $payment->customer->address->town; // DB layer will load customer & address info

uninitialized.php

<?php
/**
 * Example of possible lazy-loading in PHP
 * Added new special value called "uninitialized". When a property with this value is being read from object,
 *  __initialize($propertyName) magic method is invoked to lazy-load the value.
 */

class Foo {
    private $bar = uninitialized;
    private $lol = "lol";
    public $pub = uninitialized;
    public $blank = uninitialized;

    function getBar() {
        echo "Getter method bar, ";
        return $this->bar;
    }

    function getLol() {
        echo "Getter method lol, ";
        return $this->lol;
    }

    function getPub() {
        echo "Getter method pub, ";
        return $this->pub;
    }

    function __get($name) {
        echo "Magic getter $name, ";
        return $this->$name;
    }

    function __initialize($name) {
        if($name !== 'blank') {
            echo "Initializing $name, ";
            $this->$name = "I'm $name";
        }
        else {
            echo "Trying to initialize blank, ";
        }
    }

    function clean() {
        $this->bar = $this->lol = $this->pub = uninitialized;
    }
}


// __initialize will be called only once, on first access
$foo = new Foo;
var_dump($foo->getBar()); // Getter method bar, Initializing bar, string(7) "I'm bar"
var_dump($foo->getBar()); // Getter method bar, string(7) "I'm bar"


// magic __get is called first, and inside it's initialized
$foo = new Foo;
var_dump($foo->bar); // Magic getter bar, Initializing bar, string(7) "I'm bar"
var_dump($foo->bar); // Magic getter bar, string(7) "I'm bar"
$foo->clean();
var_dump($foo->bar); // Magic getter bar, Initializing bar, string(7) "I'm bar"
var_dump($foo->bar); // Magic getter bar, string(7) "I'm bar"


// lazy-loading of public properties
$foo = new Foo;
var_dump($foo->pub); // Initializing pub, string(7) "I'm pub"


// normal value remains as expected
$foo = new Foo;
var_dump($foo->getLol()); // Getter method lol, string(3) "lol"


// variable which cannot be initialized
$foo = new Foo;
var_dump($foo->blank); // Trying to initialize blank, undefined
var_dump($foo->blank); // Trying to initialize blank, undefined

The real reason why I want uninitialized to be assign-able could be seen in example.php of this Gist. You may have a class Customer, which has just normal properties (not with a lazy keyword as proposed by @hosiplan, nor with predefined uninitialized value). You can new that class and all properties will have nulls, as normally. Nothing changes here.

First time a new type of value would be used is when you load a $payment from database. DB layer will create instance of Customer class, assign proper id to it's $id property and uninitialized to all other properties. Then, when you access such a property for the first time, DB layer can lazy-load the whole customer instance.

You, as a programmer, don't have to ever use this special value. It will just be used for you by the DB layer, which might be easier with this support in PHP lang.

@juzna Hmm, makes sense. Still don't like it. Better make real support for proxy objects...

One approach of lazyload: https://gist.github.com/1049509

I belive there is much more magic in @md2perpe's example. And it also add some domain logic which must be present in all objects. Jan Dolecek [email protected]

…

On Mon, Jun 27, 2011 at 7:56 PM, md2perpe < ***@***.***>wrote: One approach of lazyload: https://gist.github.com/1049509 ## Reply to this email directly or view it on GitHub: https://gist.github.com/1046613