Classes

[nightowl]

When do you use an instance of a class ($db = new database();$db->query($sql)) and when do you immediately use the class itself (database::query($sql)) ?

Are there "best practices" ?

I always used instances ($db = new ...) but saw in the code of patTemplate et.al (www.php-tools.de) that they linked directly to the class, thus preventing all problems related to where to define the database connection etc...

class person {

function new() {
db::query($sql);
}

}

instead of

class person {
function person {
$this->db = new database();
}

function new() {
$this->db->query($sql);
}
}

What do you do ? When do you use what?

[Shrike]

You can call class functions statically using the :: operator, but you cannot access member variables that way, only by instantiating the class. Also on instantiation the class constructor, if present, is executed, but not when class functions are used statically. The $this operator is used to refer to the current object context, and since theres no object context when calling static methods, it does nothing 🙂

<?php
class a {
	var $a = "nothing";

/** Constructor is run when object is instantiated */
function a(){
	echo $this->a;
}
/** Member variables are not available when class is used statically */
function b(){
	echo $this->a;
}
/** Member variables can be set literally when used statically */
function c(){
	$this->a = "something";
	echo $this->a;
}
/** But not in the way you'd expect */
function d(){
	echo $this->a;
}
}

$a = new a();

a::b();
a::c();
a::d();

?>

[nightowl]

Thx for the info. Still wondering why your example return nothing for function d) while this works fine ...

<?php

class db {

function db() {
	echo "db initialised<br>";
}

function setSQL($sql) {

	$this->sql = $sql;

}

function query() {

	echo "querying db with sql $this->sql<br>";

}

}

class page {

function page() {

	echo "page initialised<br>";
}

function execQuery($sql) {

	db::setSQL($sql);
	db::query();

}

}


$page = new page;
$page->execQuery("select * from users");



?>

It output ...

page initialised
querying db with sql select * from users

as expected.

I'm puzzled with how to use interdependent classes if not by using them statically.

Like a couple of classes which all use the same database connection...

[Shrike]

Well static classes can output text no problem, and also you are passing $sql from an instantiated object, so i guess this has an effect. The following:

db::setSQL("select * from users");
db::query();

Loses the $sql output.