PHP - Does it ignore return val from constructors?

I am trying to figure out how to make an object creation fail for ease
of error handling. Oddly, I can't work out how to do it.

Here's a reduced code sample of how I hoped it would work, but it
doesn't:

class Thing {
var $error;
function Thing() {
return 0;
}
}

if (!$theThing = new Thing()) {
echo "Couldn't create the thing -" . $thing->error;
}

I guess I could set $this to false instead of returning 0. But then I
wouldn't get the benefit of the error message, unless I echoed it,
which I don't like to do in classes.

Any good way to do this?

thecrow wrote:
> I am trying to figure out how to make an object creation fail for ease
> of error handling. Oddly, I can't work out how to do it.
>
> Here's a reduced code sample of how I hoped it would work, but it
> doesn't:
>
> class Thing {
> var $error;
> function Thing() {
> return 0;
> }
> }
>
> if (!$theThing = new Thing()) {
> echo "Couldn't create the thing -" . $thing->error;
> }
>
> I guess I could set $this to false instead of returning 0. But then I
> wouldn't get the benefit of the error message, unless I echoed it,
> which I don't like to do in classes.

I have a recollection that you can't get return values from
constructors. The way around it would be something like this:

class Foo {

function Foo () {
$this->initialize();
}

function initialize() {
if (yadayadayada) {
...
}
else {
return 0;
}
}
}

/Marcin

"thecrow" <carltonbrown@hotmail.com> wrote in message
news:1109247316.134425.288660@z14g2000cwz.googlegr oups.com...
> I am trying to figure out how to make an object creation fail for ease
> of error handling. Oddly, I can't work out how to do it.
>
> Here's a reduced code sample of how I hoped it would work, but it
> doesn't:
>
> class Thing {
> var $error;
> function Thing() {
> return 0;
> }
> }
>
> if (!$theThing = new Thing()) {
> echo "Couldn't create the thing -" . $thing->error;
> }
>
> I guess I could set $this to false instead of returning 0. But then I
> wouldn't get the benefit of the error message, unless I echoed it,
> which I don't like to do in classes.
>
> Any good way to do this?
>

Doing what you're not supposed to:

class Thing {
var $error;
function Thing() {
$this = false;
}
}

Thank you for the explanation.

That leaves me with the problem, if I fail the constructor by setting
$this to false, how do I get the error information without echoing it?

I guess I can go search on that, but if anyone has any commonly used
ideas I would appreciate it.

In article <1109294863.754779.98710@g14g2000cwa.googlegroups. com>,
"thecrow" <carltonbrown@hotmail.com> wrote:

> Thank you for the explanation.
>
> That leaves me with the problem, if I fail the constructor by setting
> $this to false, how do I get the error information without echoing it?
>
> I guess I can go search on that, but if anyone has any commonly used
> ideas I would appreciate it.

Use a manual constructor:

class Thing {
function Thing {
#nothing here
}
function fetch {
if ($CanInstantiate) {
return new Thing;
} else {
return false;
}
}
}

- Alessandro

"thecrow" <carltonbrown@hotmail.com> wrote in message
news:1109294863.754779.98710@g14g2000cwa.googlegro ups.com...
> Thank you for the explanation.
>
> That leaves me with the problem, if I fail the constructor by setting
> $this to false, how do I get the error information without echoing it?
>
> I guess I can go search on that, but if anyone has any commonly used
> ideas I would appreciate it.
>

That was just a stupid PHP 4 trick. Don't use it. It doesn't work in PHP 5.

Constructors are meant for initializing an object. They are not supposed to
fail. The only reasonable way to handle a failure in a constructor is
through exception handling, which doesn't exist in PHP 4. As others have
suggested, put the code that could potentially fail in a separate function.