PHP empty() strange behaviour

Question

The following code (#1):

var_dump($myObject->getBook()->getCollection());
$testArray=Array();
var_dump($testArray);
var_dump(empty($testArray));

...will output:

array(0) { } array(0) { } bool(true)

The following code (#2):

var_dump($myObject->getBook()->getCollection());
$testArray=Array();
var_dump($testArray);
var_dump(empty($myObject->getBook()->getCollection()));

...will output:

Nothing. No error, not a single character. No nothing.

class Book{
  protected $bidArray=Array();
  public function getCollection(){
    return $this->bidArray;
  }
}

What is happening there?

Is displaying errors turned on? – Jasper Apr 21 '12 at 14:38 — Jasper, Apr 21 '12 at 14:38

score 7 · Accepted Answer · answered Apr 21 '12 at 14:39

7

empty() is not a function, although it looks like a one. It's just a special syntax that works only with variables, e.g. empty($abc). You simply cannot use expressions such as empty(123) or empty($obj->getSth()).

answered Apr 21 '12 at 14:39

Crozin

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Yeah. Just stored the return value of `getCollection()` in a variable before using `empty()`. PHP is sick. – Dyin Apr 21 '12 at 14:43
1

@Dyin *PHP is sick.* - I couldn't agree more. ;) – Crozin Apr 21 '12 at 14:44

score 3 · Answer 2 · answered Apr 21 '12 at 14:40

3

You cannot use empty() with anything other than variable (that means no function call as well).

var_dump(empty($myObject->getBook()->getCollection()));

You must have your error display turned off, as the following:

<?php

class Bar {
        function foo() {
        }
}

$B = new Bar();
empty($B->foo());

Gives

PHP Fatal error: Can't use method return value in write context in D:\cw\home\andreas\test\empty.php on line 9

Fatal error: Can't use method return value in write context in D:\cw\home\andreas\test\empty.php on line 9

On my local.

Try doing ini_set('display_errors', true) prior to your var_dump's and see if the error messages crop up

answered Apr 21 '12 at 14:40

Andreas Wong

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Tired to set `display_errors` as you mentioned. Still no output. Got fatal errors from elsewhere BTW. Using PHP 5.3.8 with XAMPP. – Dyin Apr 21 '12 at 14:46
@Dyin hmm, also try with `ini_set('error_reporting', E_ALL)` along with `display_errors`, see if that helps – Andreas Wong Apr 21 '12 at 14:47

score 2 · Answer 3 · answered Apr 21 '12 at 14:40

As on php.net

empty() only checks variables as anything else will result in a parse error. In other words, the following will not work: empty(trim($name)).

This is because empty() isn't a function, but a language construct and therefore limited to this behaviour.

score 2 · Answer 4 · edited May 23 '17 at 11:55

2

Using empty() you can't check directly against the return value of a method. More info here: Can't use method return value in write context

edited May 23 '17 at 11:55

Community

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answered Apr 21 '12 at 14:40

sthzg

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PHP empty() strange behaviour

4 Answers4