Classes and Constructors in PHP

Quick question on calling constructors

[Nick_W]

Hi

I don't seem to be able to get onto the manual this morning so here's a quickie for any that know....

if I create a constructor for a class and call it like this:

$new = new myclass();

The constructor function is executed right?

But, if I call it like this:

$new = new myclass;

Will I get an instance of the object without executing the constructor?

Many thanks

Nick

[Nick_W]

Okay, okay, I'm lazy :(

Just tested it and for any that were wondering, they are exactly the same, the construtor is called regardless of how you invoke a new instance of the object...

Nick

[jatar_k]

yep, when you create a new instance of an object it's constructor is called by default.

Otherwise it can't be constructed. ;)

[Nick_W]

heh, yes.

I was just looking for a neat way to invoke an instance for two differnent situations. One where the constructor was needed (although it could just be a regular method) and one where it was not.

No bit deal to just make a method and call when needed, but, it seemed logical at the time....

Nick

[andreasfriedrich]

As the constructor is just a method that happens to get called when a new instance of a class is created and is not even required it is indeed a good idea to use just some other method when you need a piece of code only for some instances and not for every single one.

Andreas

[jatar_k]

a class can have multiple constructors to handle different instances, can't it? (been a little bit since I did OO).

I seem to remember different constructors within a class based on how the new object was created, be it type or method.

[Nick_W]

Dont think so Jatar

Though I've done constructors that took values and acted diffently according to those values which is kinda the same..

funciton constructor($val) {
if($vall==1) {
do one thing
} else do another

You get the point ;)

Nick

[jatar_k]

maybe not php but I'm looking around on G and it seems to be true.

I remember C++ being like that. Depending on the number of params passed and what they are the object using a different constructor. Though I could also be losing my mind. ;)

[andreasfriedrich]

In Java you could indeed do something like this:

public class Aaron { 
 public Aaron(String s, int a) { 
  System.out.println('two parameter'); 
 } 
 public Aaron(String s) { 
  System.out.println('one parameter'); 
 } 
}

Aaron a = new Aaron('Carter', 15);

would print two parameter while

Aaron a = new Aaron('Carter');

would print one parameter.

However, this is not possible in PHP.

class Aaron { 
  function Aaron($str1, $str2) { 
    echo "two paras:"; 
  } 
  function Aaron($str1) { 
    echo "one para:"; 
  } 
}

This will always print "one para" no matter whether you create the instance using two parameters or just one. The second declaration of Aaron will override the first one.

Andreas

[Nick_W]

You can overload a constructor? (is that the right term?)

Nick

[andreasfriedrich]

Yes, thatīs exactly the right term: A method having the same name and being distinguished by its signature, i.e. its different types and/or numbers of arguments or arguments in different position in its argument list.

This is available in C++ and Java. At least those are the ones I know of.