is_a() vs. instanceof

20 years ago by Hans Lellelid — view source

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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

20 years ago by Dan Ostrowski — view source

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> 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

20 years ago by Alan Knowles — view source

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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:

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

20 years ago by Hans Lellelid — view source

unread

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

20 years ago by Al Baker — view source

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

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

20 years ago by Jevon Wright — view source

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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

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

20 years ago by Sean Coates — view source

unread

Dan Ostrowski 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.