copy of object is a reference in PHP5

5 Message(s) by 3 Author(s) originally posted in php programming

From: groups2

Date: Thursday, October 25, 2007

Can someone please explain the results below
We switched to PHP 5
if I make a copy of an object

<object-oriented> In {object-oriented programming}, an
	instance of the data structure and behaviour defined by the
	object's {class}.  Each object has its own values for the
	{instance variables} of its class and can respond to the
	{methods} defined by its class.

	For example, an object of the "Point" class might have
	instance variables "x" and "y" and might respond to the "plot"
	method by drawing a dot on the screen at those coordinates.

	(2004-01-26)

, and then change the variable

<programming> (Sometimes "var" /veir/ or /var/) A named memory
	location in which a program can store intermediate results and
	from which it can read it them.  Each {programming language}
	has different rules about how variables can be named, typed,
	and used.  Typically, a value is "assigned" to a variable in
	an {assignment} statement.  The value is obtained by
	evaluating an expression and then stored in the variable.  For
	example, the assignment

		x = y + 1

	means "add one to y and store the result in x".  This may look
	like a mathematical equation but the mathematical equality is
	only true in the program until the value of x or y changes.
	Furthermore, statements like

		x = x + 1

	are common.  This means "add one to x", which only makes sense
	as a state changing operation, not as a mathematical equality.

	The simplest form of variable corresponds to a single-{word}
	of {memory} or a {CPU} {register} and an assignment to a
	{load} or {store} {machine code} operation.

	A variable is usually defined to have a {type}, which never
	changes, and which defines the set of values the variable can
	hold.  A type may specify a single ("atomic") value or a
	collection ("aggregate") of values of the same or different
	types.  A common aggregate type is the {array} - a set of
	values, one of which can be selected by supplying a numerical
	{index}.

	Languages may be {untyped}, {weakly typed}, {strongly typed},
	or some combination.  {Object-oriented programming} languages
	extend this to {object} types or {classes}.

	A variable's {scope} is the region of the program source
	within which it represents a certain thing.  Scoping rules are
	also highly language dependent but most serious languages
	support both {local variables} and {global variables}.
	{Subroutine} and {function} {formal arguments} are special
	variables which are set automatically by the language runtime
	on entry to the subroutine.

	In a {functional programming} language, a variable's value
	never changes and change of state is handled as recursion over
	lists of values.

	(2004-11-16)

inside the
object the change is reflected in the copy.

Either the copy is a reference

1. <programming> An {address}, from the point of view of a
	programming language.  A pointer may be typed, with its {type}
	indicating the type of data to which it points.

	The terms "pointer" and "reference" are generally
	interchangable although particular programming languages often
	differentiate these two in subtle ways.  For example, {Perl}
	always calls them references, never pointers.  Conversely, in
	C, "pointer" is used, although "a reference" is often used to
	denote the concept that a pointer implements.

	{Anthony Hoare} once said:

	Pointers are like jumps, leading wildly from one part of the
	data structure to another.  Their introduction into high-level
	languages has been a step backward from which we may never
	recover.

	[C.A.R.Hoare "Hints on Programming Language Design", 1973,
	Prentice-Hall collection of essays and papers by Tony Hoare].

	2. <operating system> (Or "mouse pointer") An {icon}, usually
	a small arrow, that moves on the screen in response to
	movement of a {pointing device}, typically a {mouse}.  The
	pointer shows the user which object on the screen will be
	selected etc. when a mouse button is clicked.

	(1999-07-07)

to the object or the variable inside
the object is a static variable, I'm not sure what is going on, but It
does not seem like it should be doing that. Is that because of a
setting on the server

1. A program which provides some service to other ({client})
	programs.  The connection between client and server is
	normally by means of {message passing}, often over a
	{network}, and uses some {protocol} to encode the client's
	requests and the server's responses.  The server may run
	continuously (as a {daemon}), waiting for requests to arrive
	or it may be invoked by some higher level daemon which
	controls a number of specific servers ({inetd} on {Unix}).

	There are many servers associated with the {Internet}, such as
	those for {HTTP}, {Network File System}, {Network Information
	Service} (NIS), {Domain Name System} (DNS), {FTP}, {news},
	{finger}, {Network Time Protocol}.  On Unix, a long list can
	be found in /etc/services or in the {NIS} database "services".
	See {client-server}.

	2. A computer which provides some service for other computers
	connected to it via a network.  The most common example is a
	{file server} which has a local disk and services requests
	from remote clients to read and write files on that disk,
	often using {Sun}'s {Network File System} (NFS) {protocol} or
	{Novell Netware} on {PCs}.  Another common example is a {web
	server}.

	[{Jargon File}]

	(2003-12-29)

or something ?

<?$label=new myObj();
$label->settext('the text');

$copy=$label;
print_r($copy);
$label->settext('different text');
print_r($copy);

class

1. <programming> The prototype for an {object} in an
	{object-oriented language}; analogous to a {derived type} in a
	{procedural language}.  A class may also be considered to be a
	set of objects which share a common structure and behaviour.
	The structure of a class is determined by the {class
	variables} which represent the {state} of an object of that
	class and the behaviour is given by a set of {methods}
	associated with the class.

	Classes are related in a {class hierarchy}.  One class may be
	a specialisation (a "{subclass}") of another (one of its
	"{superclasses}") or it may be composed of other classes or it
	may use other classes in a {client-server} relationship.  A
	class may be an {abstract class} or a {concrete class}.

	See also {signature}.

	2. <programming> See {type class}.

	3. <networking> One of three types of {Internet addresses}
	distinguished by their most significant bits.

	3. <language> A language developed by the {Andrew Project}.
	It was one of the first attempts to add {object-oriented}
	features to {C}.

	(1995-05-01)

myObj{
var $text;
function

1. <mathematics> (Or "map", "mapping") If D and C are sets
	(the domain and codomain) then a function f from D to C,
	normally written "f : D -> C" is a subset of D x C such that:

	1. For each d in D there exists some c in C such that (d,c) is
	an element of f.  I.e. the function is defined for every
	element of D.

	2. For each d in D, c1 and c2 in C, if both (d,c1) and (d,c2)
	are elements of f then c1 = c2.  I.e. the function is uniquely
	defined for every element of D.

	See also {image}, {inverse}, {partial function}.

	2. <programming> Computing usage derives from the mathematical
	term but is much less strict.  In programming (except in
	{functional programming}), a function may return different
	values each time it is called with the same argument values
	and may have {side effects}.

	A {procedure} is a function which returns no value but has
	only {side-effects}.  The {C} language, for example, has no
	procedures, only functions.  {ANSI C} even defines a {type},
	{void}, for the result of a function that has no result.

	(1996-09-01)

settext($text){
$this->text=$text;
}

}

?>
results:
myObj Object
(
[text] => the text
)
myObj Object
(
[text] => different text
)

From: JustinCarmony

Date: Thursday, October 25, 2007

wrote in message:

Can someone please explain the results below
We switched to PHP 5
if I make a copy of an object, and then change the variable inside the
object the change is reflected in the copy.
Either the copy is a reference to the object or the variable inside
the object is a static variable, I'm not sure what is going on, but It
does not seem like it should be doing that. Is that because of a
setting on the server or something ?
<?
$label=new myObj();
$label->settext('the text');
$copy=$label;
print_r($copy);
$label->settext('different text');
print_r($copy);
class myObj{
var $text;
function settext($text){
$this->text=$text;
}
}
?>
results:
myObj Object
(
[text] => the text
)
myObj Object
(
[text] => different text
)

All objects in PHP 5, if I'm not mistaken, are always passed by
reference. Example:
<?php

class MyClass
{
public $myVar;

function __construct()
{
$this->myVar = 1;
}
}

$class1 = new MyClass();

$class2 = $class1;

$class1->myVar = 2;

echo $class2->myVar; // Outputs 2

?>

If you want to make a copy of an object, so its a new object and not a
reference is to use the clone

<jargon> 1. An exact copy of a product, made legally or
	illegally, from {documentation} or by {reverse engineering},
	and usually cheaper.

	E.g. "PC clone": a PC-BUS/{ISA}, {EISA}, {VESA}, or {PCI}
	compatible {x86}-based {microcomputer} (this use is sometimes
	misspelled "klone" or "PClone").  These invariably have much more
	bang per buck than the {IB PCM} they resemble.

	E.g. "Unix clone": An {operating system} designed to deliver a
	{Unix}-like environment without Unix licence fees or with
	additional "mission-critical" features such as support for
	{real-time} programming.

	2. <chat> A {clonebot}.

	[{Jargon File}]

	(2000-06-15)

keyword

1. One of a fixed set of symbols built into the syntax of a
	language.  Typical keywords would be if, then, else, print,
	goto, while, switch.  There are usually restrictions about
	reusing keywords as names for user-defined objects such as
	variables or procedures.  Languages vary as to what is
	provided as a keyword and what is a library routine, for
	example some languages provide keywords for input/output
	operations whereas in others these are library routines.

	2. A small set of words designed to convey the subject of a
	technical article.  Some publications specify a fixed set of
	keywords from which those for a particular article should be
	chosen.

like this:

<?

class MyClass
{
public $myVar;

function __construct()
{
$this->myVar = 1;
}
}

$class1 = new MyClass();

$class2 = clone $class1;

$class1->myVar = 2;

echo $class2->myVar;

?>

You can also explicitly code

<software> Instructions for a computer in some programming
	language, often {machine language}.  The word "code" is often
	used to distinguish instructions from {data} (e.g. "The code
	is marked 'read-only'") whereas "{software}" is used in
	contrast with "{hardware}" and may consist of more than just
	code.

	(2000-04-08)

what is to happen when an object is
cloned by using the __clone() class function. You can read more here:
http://us3.php.net/manual/en/language.oop5.cloning.php

Carmony

From: groups2

Date: Thursday, October 25, 2007

wrote in message:
wrote in message:
> Can someone please explain the results below
> We switched to PHP 5
> if I make a copy of an object, and then change the variable inside the
> object the change is reflected in the copy.
> Either the copy is a reference to the object or the variable inside
> the object is a static variable, I'm not sure what is going on, but It
> does not seem like it should be doing that. Is that because of a
> setting on the server or something ?
> <?
> $label=new myObj();
> $label->settext('the text');
> $copy=$label;
> print_r($copy);
> $label->settext('different text');
> print_r($copy);
> class myObj{
> var $text;
> function settext($text){
> $this->text=$text;
> }
> }
> ?>
> results:
> myObj Object
> (
> [text] => the text
> )
> myObj Object
> (
> [text] => different text
> )
All objects in PHP 5, if I'm not mistaken, are always passed by
reference. Example:
<?php
class MyClass
{
public $myVar;
function __construct()
{
$this->myVar = 1;
}
}
$class1 = new MyClass();
$class2 = $class1;
$class1->myVar = 2;
echo $class2->myVar; // Outputs 2
?>
If you want to make a copy of an object, so its a new object and not a
reference is to use the clone keyword like this:
<?
class MyClass
{
public $myVar;
function __construct()
{
$this->myVar = 1;
}
}
$class1 = new MyClass();
$class2 = clone $class1;
$class1->myVar = 2;
echo $class2->myVar;
?>
You can also explicitly code what is to happen when an object is
cloned by using the __clone() class function. You can read more here:http://us3.php.net/manual/en/language.oop5.cloning.php
Carmony

bummer. What I have done is create objects with numerous properties
and a function to set 1 property and then return itself.

$label=new geocellobj();
$label->setalign('right');
$label->setvalign('middle');
$label->setstyle('border:0;');

array($label->settext('unique test'), $label->settext('different
text));

I do not think cloning will help me.

From: Thomas Hamacher

Date: Thursday, October 25, 2007

groups2@xxxxxxxxxxx schrieb:
wrote in message:

You can also explicitly code what is to happen when an object is
cloned by using the __clone() class function.

$label=new geocellobj();
$label->setalign('right');

array($label->settext('unique test'), $label->settext('different
text));

I do not think cloning will help me.

Well, just clone the objects before storing them into the array:

array(clone $label->settext(...), ...)

From: groups2

Date: Friday, October 26, 2007

wrote in message:

grou...@xxxxxxxxxxx schrieb:
wrote in message:
You can also explicitly code what is to happen when an object is
cloned by using the __clone() class function.
> $label=new geocellobj();
> $label->setalign('right');
> array($label->settext('unique test'), $label->settext('different
> text));
> I do not think cloning will help me.
Well, just clone the objects before storing them into the array:
array(clone $label->settext(...), ...)

Ok thanks that works great.

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