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php

is_a() vs. instanceof

php.internals

Hans Lellelid

22 years ago

I like the new $obj instanceof ClassName way of checking class /
interface types, .... but this method does have one major drawback
compared to the old is_a() approach:

The class must be loaded in order to perform an instanceof check!

Apparently is_a() has also been deprecated,  so that an E_STRICT error
is thrown.  This means that to check types of classes and remain
E_STRICT compliant I have to load & parse every class.  It's not hard to
imagine situations (and experience has shown this to be the case) where
this limitation can lead to a lot of extra file i/o and parsing -- and
also E_WARNING if the file couldn't be included, etc.

Is is possible to have instanceof not require the class to be loaded?
or perhaps just have is_a() not trigger an E_STRICT error?

Thanks,
Hans

Dan Ostrowski

22 years ago

On Tuesday 10 August 2004 7:36 pm, Hans Lellelid wrote:

> I like the new $obj instanceof ClassName way of checking class /
> interface types, .... but this method does have one major drawback
> compared to the old is_a() approach:
>
>     The class must be loaded in order to perform an instanceof check!
>

Isn't that the point? is_a() and instanceof are ways of checking the class of
an object at runtime where it could be any number of things. ( And here I'm
assuming you mean instantiated instead of "loaded"? )

If you don't have an instantiated object.. what do you have? A class! And THAT
can be checked at "compile" ( or in this case write ) time. There's something
wrong with my code, if I'm thinking of this right, if I have no idea if class
A is a subclass of class B.

Now, if I'm passed random objects, I may want to know of which types they
are... which is where these functions/builtins come in...

Am I misunderstanding you?


Dan Ostrowski

Alan Knowles

22 years ago

I think he's referening to something like this (which is common in pear):

$x = $someobj->somemethod();
if ($x instanceOf PEAR_Error) {
.......
}

while that code is redundant in the case of exceptions, it is still a
valid situation.. that $x may be a valid return, and PEAR_Error was
never loaded..

Regards
Alan




Dan Ostrowski wrote:

Hans Lellelid

22 years ago

Alan Knowles wrote:

> I think he's referening to something like this (which is common in pear):
>
> $x = $someobj->somemethod();
> if ($x instanceOf PEAR_Error) {
>   .......
> }
>
> while that code is redundant in the case of exceptions, it is still a
> valid situation.. that $x may be a valid return, and PEAR_Error was
> never loaded..

Yup, that's exactly what I'm talking about.

I want to be able to do this:

if ($db instanceof DBPostgres) {
/// do something funky specific to Postgres
}

If My DB adapter is DBMySQL, I don't want to load the DBPostgres adapter
just so I can test whether my object is of that type ...

and checking first whether class_exists('DBPostgres') just seems kinda
kludgy & straying from the "problem domain" ... especially since $db
instanceof DBPostgres would *always* be false if DBPostgres isn't loaded.

Hans

Al Baker

22 years ago

I agree, that's the exact behavior I would like as well and what most
people would expect.

Al

On Wed, 2004-08-11 at 23:52 -0400, Hans Lellelid wrote:

Jevon Wright

22 years ago

What about:

if (get_class($obj) == "unloadedclass") {
// blah
}

Jevon

----- Original Message -----
From: "Al Baker" <ajb732@comcast.net>
To: "Hans Lellelid" <hans@velum.net>
Cc: "Dan Ostrowski" <dan@ostrowski.cc>; <internals@lists.php.net>
Sent: Thursday, August 12, 2004 9:58 PM
Subject: Re: [PHP-DEV] is_a() vs. instanceof

> I agree, that's the exact behavior I would like as well and what most
> people would expect.
>
> Al
>
> On Wed, 2004-08-11 at 23:52 -0400, Hans Lellelid wrote:
> > Alan Knowles wrote:
> >
> > > I think he's referening to something like this (which is common in

pear):

> > >
> > > $x = $someobj->somemethod();
> > > if ($x instanceOf PEAR_Error) {
> > >   .......
> > > }
> > >
> > > while that code is redundant in the case of exceptions, it is still a
> > > valid situation.. that $x may be a valid return, and PEAR_Error was
> > > never loaded..
> >
> >
> > Yup, that's exactly what I'm talking about.
> >
> > I want to be able to do this:
> >
> > if ($db instanceof DBPostgres) {
> >    /// do something funky specific to Postgres
> > }
> >
> > If My DB adapter is DBMySQL, I don't want to load the DBPostgres adapter
> > just so I can test whether my object is of that type ...
> >
> > and checking first whether class_exists('DBPostgres') just seems kinda
> > kludgy & straying from the "problem domain" ... especially since $db
> > instanceof DBPostgres would *always* be false if DBPostgres isn't

loaded.

Sean Coates

22 years ago

Dan Ostrowski wrote:

> On Tuesday 10 August 2004 7:36 pm, Hans Lellelid wrote:
>>    The class must be loaded in order to perform an instanceof check!

*snip*

> Am I misunderstanding you?
>

consider the following:

<?php

class Foo {}

$foo = unserialize('O:3:"Foo":0:{}');

echo '$foo is_a Foo? '. (is_a($foo, 'Foo') ? 'yes' : 'no') ."\n";
echo '$foo instanceof Foo? '. ($foo instanceof Foo ? 'yes' : 'no') ."\n";

?>
outputs:
$foo is_a Foo? yes
$foo instanceof Foo? yes

and
<?php

//class Foo {}

$foo = unserialize('O:3:"Foo":0:{}');

echo '$foo is_a Foo? '. (is_a($foo, 'Foo') ? 'yes' : 'no') ."\n";
echo '$foo instanceof Foo? '. ($foo instanceof Foo ? 'yes' : 'no') ."\n";

?>
outputs:
$foo is_a Foo? no

Fatal error: Class 'Foo' not found in
/home/sean/phpdoc/scripts/tmp/is_a.php on line 8

---

I realize that is_a is deprecated, but it's more convenient in this
situation.

S