Suppose I have:

class A {
function __construct() {
$this->val = true;
}
}

$a = new A();

if ($a) {
echo 'some text';
}

When I test "if ($a)", I want the class A to respond with the value of
$this->val, which is true at the moment.

Is this possible?

wswilson schreef:
> Suppose I have:
>
> class A {
> function __construct() {
> $this->val = true;
> }
> }
>
> $a = new A();
>
> if ($a) {
> echo 'some text';
> }
>
> When I test "if ($a)", I want the class A to respond with the value of
> $this->val, which is true at the moment.
>
> Is this possible?

$a is an instance of your class, not a boolean.
So don't care if it is possible, care how OOP works. :-)

In your example you only populate some instance variable named val with
value true. $a will never return that unless you ask it to.

Regards,
Erwin Moller

On Thu, 27 Mar 2008 14:33:35 +0100, wswilson <wswilson@gmail.com> wrote:

> Suppose I have:
>
> class A {
> function __construct() {
> $this->val = true;
> }
> }
>
> $a = new A();
>
> if ($a) {
> echo 'some text';
> }
>
> When I test "if ($a)", I want the class A to respond with the value of
> $this->val, which is true at the moment.
>
> Is this possible?

Nope, that kind of overloading cannot be done in PHP atm.
What you can do is:
- control how an object is evaluated in a string context with the magic
__toString() function.
- you can have some control over how an object is evaluated in an array
context with for instance
<http://www.php.net/~helly/php/ext/spl/classArrayIterator.html>

.... however, for boolean castings default type casting applies, see
<http://nl2.php.net/manual/en/language.types.boolean.php#language.types.boolean. casting>

Given no further context, I see no clear reason why you can't call
if($a->val) instead of if($a).
--
Rik Wasmus

Rik Wasmus wrote:
> On Thu, 27 Mar 2008 14:33:35 +0100, wswilson <wswilson@gmail.com> wrote:
>
>> Suppose I have:
>>
>> class A {
>> function __construct() {
>> $this->val = true;
>> }
>> }
>>
>> $a = new A();
>>
>> if ($a) {
>> echo 'some text';
>> }
>>
>> When I test "if ($a)", I want the class A to respond with the value of
>> $this->val, which is true at the moment.
>>
>> Is this possible?
>
> Nope, that kind of overloading cannot be done in PHP atm.
> What you can do is:
> - control how an object is evaluated in a string context with the magic
> __toString() function.
> - you can have some control over how an object is evaluated in an array
> context with for instance
> <http://www.php.net/~helly/php/ext/spl/classArrayIterator.html>
>
> ... however, for boolean castings default type casting applies, see
> <http://nl2.php.net/manual/en/language.types.boolean.php#language.types.boolean. casting>
>
>
> Given no further context, I see no clear reason why you can't call
> if($a->val) instead of if($a).

Where has he defined $val? Shouldn't he have declared it as a class
variable? Given that (and declared private since it doesn't make much
sense to declare a class value as public from an data hiding point of
view) he would need an accessor function like getVal() { return
$this->val; } and call if($a->getVal()) .

On Mar 27, 1:05pm, "Rik Wasmus" <luiheidsgoe...@hotmail.com> wrote:
> On Thu, 27 Mar 2008 14:33:35 +0100, wswilson <wswil...@gmail.com> wrote:
> > Suppose I have:
>
> > class A {
> > function __construct() {
> > $this->val = true;
> > }
> > }
>
> > $a = new A();
>
> > if ($a) {
> > echo 'some text';
> > }
>
> > When I test "if ($a)", I want the class A to respond with the value of
> > $this->val, which is true at the moment.
>
> > Is this possible?
>
> Nope, that kind of overloading cannot be done in PHP atm.
> What you can do is:
> - control how an object is evaluated in a string context with the magic
> __toString() function.
> - you can have some control over how an object is evaluated in an array
> context with for instance
> <http://www.php.net/~helly/php/ext/spl/classArrayIterator.html>
>
> ... however, for boolean castings default type casting applies, see
> <http://nl2.php.net/manual/en/language.types.boolean.php#language.type...>
>
> Given no further context, I see no clear reason why you can't call
> if($a->val) instead of if($a).
> --
> Rik Wasmus

Thanks. I was look for a shortcut to testing on $a->val. Long story
why I would want this shortcut... Oh well.

On Thu, 27 Mar 2008 18:44:29 +0100, sheldonlg <sheldonlg> wrote:
> Rik Wasmus wrote:
>> On Thu, 27 Mar 2008 14:33:35 +0100, wswilson <wswilson@gmail.com> wrote:
>>
>>> Suppose I have:
>>>
>>> class A {
>>> function __construct() {
>>> $this->val = true;
>>> }
>>> }
>>>
>>> $a = new A();
>>>
>>> if ($a) {
>>> echo 'some text';
>>> }
>>>
>>> When I test "if ($a)", I want the class A to respond with the value of
>>> $this->val, which is true at the moment.
>>>
>>> Is this possible?
>> Nope, that kind of overloading cannot be done in PHP atm.
>> What you can do is:
>> - control how an object is evaluated in a string context with the magic
>> __toString() function.
>> - you can have some control over how an object is evaluated in an array
>> context with for instance
>> <http://www.php.net/~helly/php/ext/spl/classArrayIterator.html>
>> ... however, for boolean castings default type casting applies, see
>> <http://nl2.php.net/manual/en/language.types.boolean.php#language.types.boolean. casting>
>> Given no further context, I see no clear reason why you can't call
>> if($a->val) instead of if($a).
>
> Where has he defined $val?

He hasn't defined val, but it is assigned a value in the constructor, so
it automatically becomes a public property.

> Shouldn't he have declared it as a class variable?

He should have, however, this is not strictly necessary in PHP.
<?php
class foo{}
$a = new foo();
$a->bar = 'foz';
echo $a->bar;
?>

> Given that (and declared private since it doesn't make much sense to
> declare a class value as public from an data hiding point of view) he
> would need an accessor function like getVal() { return $this->val; }
> and call if($a->getVal()) .

Ideally yes, if he needs absolute control. A construct using the __get()
function (and limitations on __set()) is also very common.
--
Rik Wasmus

wswilson wrote:

> class A {
> function __construct() {
> $this->val = true;
> }
> }
>
> $a = new A();
>
> if ($a) {
> echo 'some text';
> }
>
> When I test "if ($a)", I want the class A to respond with the value of
> $this->val, which is true at the moment.
>
> Is this possible?

I can get you close...

class A
{
function __contruct ()
{
$this->val = true;
}

function __toString ()
{
return (string)$this->val;
}
}

$a = new A();
if ("$a") echo 'some text';

Note the quote marks on the last line though -- this forces $a to be
evaluated as a string, so PHP calls __toString to cast the object into a
string. __toString in turn casts $this->val as a string.

This won't work in PHP 5.0.x/5.1.x -- requires PHP 5.2.x because of the
frankly bizarre behaviour of the __toString magic method in PHP prior to
5.2.0.

Now it would be absolutely beautiful if PHP has other magic methods to
cast to other types (e.g. __toBoolean, __toArray, __toNumeric, etc) but
alas it does not.

--
Toby A Inkster BSc (Hons) ARCS
[Geek of HTML/SQL/Perl/PHP/Python/Apache/Linux]
[OS: Linux 2.6.17.14-mm-desktop-9mdvsmp, up 1 day, 21:30.]

Best... News... Story... Ever!
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