object default value in constructor

[Janez Cerar]

I'm trying to write a class with a constructor that takes a single object
parameter. So far so good, but I can't for the life of me make the parameter
optional. I understand how to do it with a numerical or textual parameter,
but not with an object. I tried null, but it doesn't work.

class A
{
}

class B
{
function B($a = ???)
{
if (!isset($a)) $a = new A;
}
}

Any ideas?

Jaka

[Nikolai Chuvakhin]

"Janez Cerar" <ja*********@email.removethis.si> wrote
in message news:<9K*******************@news.siol.net>...

I'm trying to write a class with a constructor that takes a single object
parameter.
Why? Isn't it easier to just extend the class?
So far so good, but I can't for the life of me make the parameter
optional.

class A
{
}

class B
{
function B($a = ???)
{
if (!isset($a)) $a = new A;
}
}

Try this instead:

class A {
function A () {}
}
class B extends A {}

Since you defined no constructor for B, new B will simply call the
constructor for A (in PHP 4, at least).

Cheers,
NC

[Phil Roberts]

With total disregard for any kind of safety measures [e-mail]
(Nikolai Chuvakhin) leapt forth and uttered:

Since you defined no constructor for B, new B will simply call
the constructor for A (in PHP 4, at least).

Not strictly true. The parent constructor is not called by default,
it has be called explicitly.

class ClassOne {
var $number;
function ClassOne() {
$this->number = 2;
}
}

class ClassTwo extends ClassOne {
function ClassTwo() {
# Call the parent constructor
parent::ClassOne();
}

function classMethod() {
return $this->number;
}
}

$obj =& new ClassTwo;

# Will echo '2';
echo $obj->classMethod();

--
There is no signature.....

[André Næss]

Janez Cerar:

I'm trying to write a class with a constructor that takes a single object
parameter. So far so good, but I can't for the life of me make the
parameter optional. I understand how to do it with a numerical or textual
parameter, but not with an object. I tried null, but it doesn't work.

class A
{
}

class B
{ function B($a = null) { if(!$a) { $a = new A(); } }
}

isset() checks if a variable is set or not. A variable which is set to null
is of course set. null is equivalent to false.

André Næss

[Nikolai Chuvakhin]

Phil Roberts <ph*****@HOLYflatnetSHIT.net> wrote
in message news:<Xn*************************@206.127.4.22>...

With total disregard for any kind of safety measures [e-mail]
(Nikolai Chuvakhin) leapt forth and uttered:

Since you defined no constructor for B, new B will simply call
the constructor for A (in PHP 4, at least).

Not strictly true. The parent constructor is not called by default,
it has be called explicitly.

The parent constructor IS called by default, if the child class
has no constructor defined:

...in PHP 4... If a class has no constructor, the constructor
of the base class is being called, if it exists.

http://php.net/manual/en/language.oop.constructor.php

This is really easy to test:

class A {
var $one;
var $two;
function A () {
$this->one = 'String One';
$this->two = 'Sting Two';
}
}

class B extends A {
function show () {
echo 'Field one = ', $this->one, "\r\n";
echo 'Field two = ', $this->two, "\r\n";
}
}

$b = new B();
$b->show();

The above code snippet prints:

Field one = String One
Field two = Sting Two

Cheers,
NC