PHP5 - Error when calling class property as function

Question

$f = function($v) {
    return $v + 1;
}

echo $f(4);
// output -> 5

The above works perfectly fine. However, I cannot reproduce this correctly when f is a property of a class.

class MyClass {
    public $f;

    public function __construct($f) {
        $this->f = $f;
    }

    public function methodA($a) {
        echo $this->f($a);
    }
}

// When I try to call the property `f`, PHP gets confused
// and thinks I am trying to call a method of the class ...
$myObject = new myClass($f);
$myObject->methodA(4);

The above will result in an error:

Call to undefined method MyClass::f()

@AlivetoDie `f` is not a method, it is a function stored in a variable passed to the constructor as a class property — ma77c, May 01 '18 at 13:15

Nigel Ren · Accepted Answer · 2018-05-01T13:21:36.690

5

I think the problem is that it is trying to make sense of

echo $this->f($a);

And as you've found it wants to call a member function f in the class. If you change it to

echo ($this->f)($a);

It interprets it as you want it to.

PHP 5.6 Thanks to ADyson for the comment, think this works

$f = $this->f;
echo $f($a);

edited May 01 '18 at 13:21

answered May 01 '18 at 13:15

Nigel Ren

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https://eval.in/997679 – Alive to die - Anant May 01 '18 at 13:17
maybe worth noting this only works in PHP7 – ADyson May 01 '18 at 13:17
I thought that would work, but it results in a syntax error `unexpected '('` – ma77c May 01 '18 at 13:17
2

@AlivetoDie the assumption is that the input is a function... e.g. https://eval.in/997678 – ADyson May 01 '18 at 13:18
@TT4M.C see my comment - are you using PHP 5? https://eval.in/997680 shows it fails in PHP 5, but https://eval.in/997678 shows it works in PHP 7 – ADyson May 01 '18 at 13:18
@ADyson Yes, I am using PHP 5.6 – ma77c May 01 '18 at 13:19
@TT4M.C in that case you cannot use this syntax unfortunately. – ADyson May 01 '18 at 13:19
`$f = $this->f; echo $f($a);` in PHP5 you can assign the property to a variable first ... then it works – nimmneun May 01 '18 at 13:21
@NigelRen sorry just seen your update, in the meantime I had posted an answer along the same lines. Although it seems the nominated dupe covers both cases already. – ADyson May 01 '18 at 13:24

score 2 · Answer 2 · answered May 01 '18 at 13:23

While Nigel Ren's answer (https://stackoverflow.com/a/50117174/5947043) will work in PHP 7, this slightly expanded syntax will work in PHP 5 as well:

class MyClass {
    public $f;

    public function __construct($f) {
        $this->f = $f;
    }

    public function methodA($a) {
      $func = $this->f;
      echo $func($a);
    }
}

$f = function($v) {
    return $v + 1;
};

$myObject = new myClass($f);
$myObject->methodA(4);

See https://eval.in/997686 for a working demo.

PHP5 - Error when calling class property as function

2 Answers2