Allow non-variable arguments to empty()

2012/4/10 Nikita Popov nikita.ppv@googlemail.com

Hey internals!

Currently the empty() language construct only works on variables. You
can write if (empty($array)) but not empty if (empty(getSomeArray()).

The original reason for this restriction probably is that - in a way -
it "doesn't make sense" to pass anything but a variable to empty() as
you could just use the ! operator in this case. if
(empty(getSomeArray())) is logically equivalent to if
(!getSomeArray()).

I'd like to propose to change empty() to accept arbitrary expressions.

The reason is simple: Even though it is possible to write if
(!getSomeArray()) with the same effect, if (empty(getSomeArray()))
reads much nicer. !getSomeArray() to me somehow implies that
getSomeArray() may return a bool(false) or something like that. On the
other hand empty(getSomeArray()) seems naturally fit for checking for
empty arrays.

Another reason is that currently you get a very obscure error message
if you try to use empty() on a function return value: "Can't use
function return value in write context". Aha. Where did I try to write
to the return value?!

So, what do you think?

I think this is a useful simplification of the language, removing an
unnecessary exception. Would it also make sense to make empty() into a
library function instead of a language construct? That would not result in
any BC break as far as I can see, but would allow some things that are
currently impossible (e.g., a method called "empty") and further simplify
the language.

Nikita

PS: The patch is trivial: https://gist.github.com/2355274

Hi!

Currently the empty() language construct only works on variables. You
can write if (empty($array)) but not empty if (empty(getSomeArray()).

The original reason for this restriction probably is that - in a way -
it "doesn't make sense" to pass anything but a variable to empty() as
you could just use the ! operator in this case. if
(empty(getSomeArray())) is logically equivalent to if
(!getSomeArray()).

Don't see any problem with that, looks good. Please add some tests
(including function calls and some expressions) and make a pull request.

Stanislav Malyshev, Software Architect
SugarCRM: http://www.sugarcrm.com/
(408)454-6900 ext. 227

Sent from my iPad

在 2012-4-11，6:54，Nikita Popov nikita.ppv@googlemail.com 写道：

Hey internals!

Currently the empty() language construct only works on variables. You
can write if (empty($array)) but not empty if (empty(getSomeArray()).

The original reason for this restriction probably is that - in a way -
it "doesn't make sense" to pass anything but a variable to empty() as
you could just use the ! operator in this case. if
(empty(getSomeArray())) is logically equivalent to if
(!getSomeArray()).

I'd like to propose to change empty() to accept arbitrary expressions.

The reason is simple: Even though it is possible to write if
(!getSomeArray()) with the same effect, if (empty(getSomeArray()))
reads much nicer. !getSomeArray() to me somehow implies that
getSomeArray() may return a bool(false) or something like that. On the
other hand empty(getSomeArray()) seems naturally fit for checking for
empty arrays.
+1 for this, but what about is set? They shou be consistent, :)

Thanks

Another reason is that currently you get a very obscure error message
if you try to use empty() on a function return value: "Can't use
function return value in write context". Aha. Where did I try to write
to the return value?!

So, what do you think?

Nikita

PS: The patch is trivial: https://gist.github.com/2355274

Currently the empty() language construct only works on variables. You
can write if (empty($array)) but not empty if (empty(getSomeArray()).

I've mentioned this thought off-list already but let's discuss it
officially:

A fear I have is that this makes empty more looking like a function,
while not being one. Right now one notices quite quickly that it is
something else. Things like $check = $condition ? "empty" : "isset";
$check($bar); trigger an even more confusing error (Call to undefined
function)

I'm not sure whether that's a strong argument, but I guess it's good
enough to be noted :-)

johannes

Another reason is that currently you get a very obscure error message
if you try to use empty() on a function return value: "Can't use
function return value in write context". Aha. Where did I try to write
to the return value?!

On the line number indicated in the message :-)

More seriously, if the guts of PHP can easily detect when you are not
really write context versus this, just fix the error message to
something more meaningful.

--
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I don't see the point of empty( function() ).

You tipically use empty on values that holds information you want to use
later in the program flow (a string, an integer). That means you'd better
extract it to a variable because you want to avoid calling twice a function
that provides this value.
You don't always need the value.

Browsing around Google it seems that one of the most common source of
the function call in write context error is people trying to do
if(empty(trim($xyz)). You don't necessarily need the result of
trim($xyz), so it's reasonable not to save it into a temporary
variable.

Another example for example would be a function like this:

public function isValid() {
if (...) { $this->addError('xyz'); }
if (...) { $this->addError('abc'); }
if (...) { $this->addError('foo'); }
if (...) { $this->addError('bar'); }

return empty($this->getErrors());

}

Furthermore you don't necessarily have to throw the return value away.
For example I commonly write code like this:

if (null === $result = $this->foo()) {
throw new Exception(...);
}
$result->doSomething();

You can do something similar with empty():

if (empty($values = $this->getValues()) {
return;
}
$this->doSomethingWith($values);

I know, not everyone likes that kind of coding style, but I think it
has it's uses.

Nikita