Passing by reference

[The Red Guy]

Hi

I want to know when I should pass by reference (in oop), can anyone provide an answer for that? Also, everything in the constructor of a class gets executed like in procedural programming am I right (unlike the other functions which only execute when they are called?)

[Dr Livingston]

Umm.... Kind of hard for me to explain, though I'll instead show some example script ?

.
.
$dom = domxml_new_doc('1.0');
            $pageWidget = & new pageWidget(& $dom);
            $pageWidget -> create(); // page skeleton
            #
            $title = & new titleWidget(& $dom);
            $title -> create($action['PAGE.TITLE']);
            $pageWidget -> addHead($title -> fetch());
            $style = & new cssLinkWidget(& $dom);
            $style -> create($css);
            $pageWidget -> addHead($style -> fetch());
            #
            $pageGenerator = & new $this -> view(& $pageWidget, & $dom);
            #
            echo($pageWidget -> show());
.
. 

Above, notice that I use references for the object pageGenerator ? If so, on executing this class the results from that class are automatically passed back to the class [snippet above] ready to be ECHOed;

Whereas If I hadn't used references on the object pageGenerator and it's parameters then the content generated by this class [pageGenerator] wouldn't I believe be passed back automatically.

Also on your second point about a class constructor ? You are correct

Hope this has helped to explain references; maybe reading about references over at HarryF's site would also help you ?

www.phppatterns.com

[The Red Guy]

Still not sure, but do references help to increase efficiency?

edit: after reading around, found out the advantages, but where would it's practical uses be? And can someone explain why would I return a reference? Thanks!

[Dr Livingston]

Umm... You do not return a reference; You just use it

The

 & 

in front of a variable as in my example script is the actual reference ? To your question of advantages I'd definitely say that there is an advantage when using Objects and Arrays as your most likely to be dealing with a large amount of data ?

Better then to pass this data by references as apposed to passing by a copy of the data no ?

[Stefano F.]

References are used in the following situations:

• to avoid passing a copy (of a large amount) of data (see. expl. of Dr Livingston), hence the execution of the script is boosted
• to be in the position to manipulate the original container of the data ... pay attention!

Umm... You do not return a reference; You just use it

Well, acutally you can return a reference, if you define the signature of the function/method as:

function & returnReference() {
   
   // do something and return a variable
} 

Take notice that in PHP5 objects are always passed by reference .

[Dr Livingston]

if you define the signature of the function/method as

Sorry, my mistake - Didn't realise that a reference could be returned ?

Thanks Stefano F for pointing that out

[The Red Guy]

Let's say I've a method getObject ($param), and another displayObject ($param). How do I make $param modify to a variable in a class, and then affect the other? Like if I input $param to be 'foo', then can I pass the reference to $this->param, then in turn the $param in displayObject() can be passed by reference instead? How do I do that? Thanks!

[The Red Guy]

Also, can anyone explain what goes on in something like while (list($key,$value) = each($array))?

[website]

Also, can anyone explain what goes on in something like while (list($key,$value) = each($array))?

Then you are simply getting the key and value of the current index/key in the array and then incrementing it, it works just like

foreach ($array as $key => $value) { } 

some comments in the manual that can explain further.

[The Red Guy]

Then you are simply getting the key and value of the current index/key in the array and then incrementing it, it works just like

foreach ($array as $key => $value) { } 

some comments in the manual that can explain further.

Thanks! Then what are the differences between the two, in what situation is one preferred over the other? Also, regarding my question can someone answer it?

Let's say I've a method getObject ($param), and another displayObject ($param). How do I make $param modify to a variable in a class, and then affect the other? Like if I input $param to be 'foo', then can I pass the reference to $this->param, then in turn the $param in displayObject() can be passed by reference instead? How do I do that? Thanks!

[Dr Livingston]

Umm.... If I remember properly from the manual ?

.
.
list($a, $b, $c, $d) = each(mysql_fetch_array($sql));
.
. 

This would, assume you have 4 fields in a table, put that particular row into the variables inside the list(...) no ?

As to you original question it's too confusing for me to get my head around at the moment...

I'm seriously lacking some decent sleep at the moment

[website]

Dr, I belive this does not work, or at least you wouldn't get the desired results.

What does each() do?
each() takes the element which the internal pointer of the array points to and returns its key and value as an array on the form of
[0] => key
[1] => value
[key] => key
[value] => value
then it increments the internal pointer (then to the next element).

Example:

$array = array('value1', 'value2', 'key3' => 'value3');
//now the pointer of the array points to the first element
$arr1 = each($array);
/*
print_r($arr1) would show something like:
Array(
  [0] => 0
  [1] => value1
  [key] => 0
  [value] => value1
)
*/
$arr2 = each($array);
/*
print_r($arr2) would show something like:
Array(
  [0] => 1
  [1] => value2
  [key] => 1
  [value] => value2
)
*/
$arr3 = each($array);
/*
print_r($arr3) would show something like:
Array(
  [0] => key3
  [1] => value3
  [key] => key3
  [value] => value3
)
*/ 

As you see you could do the same with foreach().
I have rarely used each() although it does happen, it could be useful when you need some for loop or something. Imagine something like this:

for ($i = 0; $i < count($arr); $i++) {
list($key, $value) = each($arr);
/* do something */ } 

As to what Dr Livingston was doing you would do it somehow like this:

$sql = 'SELECT col1, col2, col3 FROM table';
$rslt = mysql_query($sql);
//because mysql_fetch_row returns the columns as keys in the array we'll use that (mysql_fetch_array can also be used);
while (list($col1, $col2, $col3) = mysql_fetch_row($rslt)) { } 

About the second question, I am not sure what you are asking but here is some code that might clear something?

class Test {
  var $test;

  function assignTest($test) {
    $this->test =& $test;
  }

  function printTest() {
    echo $this->test;
  }
}

$test = 'A';

$obj = new Test();
$obj->assignTest(&$test);
$test = 'B';
$obj->printTest();
//will echo B 

Hope this helps...

[Dr Livingston]

while (list($col1, $col2, $col3) = mysql_fetch_row($rslt)) { }

Umm.... Sorry I couldn't exactly remember from what I had read in the manual ...

If I remember properly from the manual ?

I knew it was down that route, so to speak

[The Red Guy]

I've one last query, for the code below I'm trying to evaluate whether the supplied parameter of a function exists in an array. Is this correct?

function getProfile ($select_team='') {
        
        if ($select_team == (in_array($_GET['act'], $this->team))) {
//do some code
        }
        else {
//do some code
        }
        return $this->select_team['results_sql'];
    } 

[Dr Livingston]

I just don't get your OOP -

$this->team 

I assume you are referring to a class property although there is no referrence to an object it's self yes ?

Something is way wrong with your example...

[website]

I've one last query, for the code below I'm trying to evaluate whether the supplied parameter of a function exists in an array. Is this correct?

function getProfile ($select_team='') {
        
        if ($select_team == (in_array($_GET['act'], $this->team))) {
//do some code
        }
        else {
//do some code
        }
        return $this->select_team['results_sql'];
    } 

if $this->team is the array you are searching, $_GET['act'] is the string/number you are checking if exists in array and $select_team is a boolean variable it is ok.

But if I understand you correctly you are checking if $select_team exists in the $this->teams array you should propably do something like

if (in_array($select_team, $this->team)) { } 

But then I don't understand where $_GET['act'] comes into things. If you would describe your problem in more detail it would be easier for us to help you.

[The Red Guy]

Ah thanks, but I've edited out all the variables and such, there's a var $team = array(). I would like to take the value of $select_team parameter given to the function, and check whether it is in a database, which is specified in $team[]. Thus I want to check is viewteam.php?act=teamname exists by using $_GET['act']. Next I'd automate the process by checking against whether in_array returns true, so that I can know what query to execute based on the team specified.

[website]

so you want to check first if $_GET['act'] exists, if it exists use it, else use the $select_team var that can be passed to the function, then compare that against the array?

so something like:

function getProfile ($select_team='') {
        $team = isset($_GET['act']) ? $_GET['act'] : $select_team;

        if ((in_array($team, $this->team))) {
//do some code
        }
        else {
//do some code
        }
        return $this->select_team['results_sql'];
    } 

would do the trick?

[The Red Guy]

Thanks! I solved it using another method, got rid of some useless code. Once again thanks for your help!