PHP fatal error Can't use method return value in write context

Question

I have seen this question being asked many times, but I am yet confused and came across something similar condition. I am not sure if this and my context are same or not, as long as I am convinced this is a different scenario or else I might have misunderstood the explanation. O.k. here is my scenario:

$amount = isset($cost->getCostAmount()) ? $cost->getCostAmount() : 0;

Function costAmount() is dynamically added during run-time and it may or may not exist. So I need to first check if my function exists or not and rest is pretty clear. But now in this case I get a fatal error:

Fatal error: Can't use method return value in write context in ..../file.php

Now if I do something like this:

$amount = $cost->getCostAmount() ? $cost->getCostAmount() : 0;

Obviously I would get an error:

Call to undefined method: getCostAmount

if the function doesn't exist. What could be a possible solution for this? Explanation will be considered helpful.

Request: Please add an adequate comment to why the question has been downvoted so that I would be able to improve my questions, in the future.

It means there is no method getCostAmount(), what is $cost ? — Mihai Iorga
– Mihai Iorga, Commented Aug 26, 2012 at 11:37
@BurhanKhalid Yes I have already tried that, it doesn't work. — ro ko
– ro ko, Commented Aug 26, 2012 at 11:43
@roko $cost has to be an initialized class for that to work. — Mihai Iorga
– Mihai Iorga, Commented Aug 26, 2012 at 11:44

Peter · Accepted Answer · 2012-08-26 11:42:41Z

8

change this:

$amount = isset($cost->getCostAmount()) ? $cost->getCostAmount() : 0;

to..

$amount = method_exists($cost, 'getCostAmount') ? $cost->getCostAmount() : 0;

because this piece of code isset($cost->getCostAmount()) is executing method getCostAmount even if it doesn't exist

answered Aug 26, 2012 at 11:42

Peter

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Comments

Shiplu Mokaddim · Accepted Answer · 2012-08-26 11:56:46Z

4

isset requires you pass a variable to it not a function. It can not check whether the return value is set.

You should use it like this,

$cost_amount = $cost->getCostAmount();
$amount = isset($cost_amount) ? $cost_amount : 0;

Even this code does not make sense. Because here $cost_amount will be always set. If getCostAmount returns null or empty string you should check it that way.

$cost_amount = $cost->getCostAmount();
$amount = !is_null($cost_amount) ? $cost_amount : 0;

Also your code does not find getCostAmount function. If you know this is declared somewhere include it. If this method is generated dynamically you can check by using method_exists.

 $amount = method_exists($cost, 'getCostAmount')? $cost->getCostAmount(): 0;

edited Aug 26, 2012 at 11:56

answered Aug 26, 2012 at 11:47

Shiplu Mokaddim

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2 Comments

ro ko Over a year ago

Thanks for the "isset requires you pass a variable to it not a function" but seems like you didn't get my context here, this would also return that the function doesn't exist.

ro ko Over a year ago

yes now it would work ofcourse and I am very thankful as well but I donot know if you were in too much hurry but this came after I don't even know how many edits :) And no it wasn't that I hadn't tried it properly because when I last read it you only had two lines of code and that didn't make too much sense, infact those things were already mentioned in the question. Yet +1 for the explanations :)

tomsv · Accepted Answer · 2012-08-26 11:38:12Z

1

Try changing isset() to function_exists()

answered Aug 26, 2012 at 11:38

tomsv

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1 Comment

lanzz Over a year ago

If that's the only change, the method invocation will still be present and the error message will stay exactly the same; besides, function_exists() will not work as you expect when used on a method and not a plain function.

Romain · Accepted Answer · 2012-08-26 11:44:47Z

0

You can use: method_exists (http://www.php.net/manual/en/function.method-exists.php) in the following way:

var_dump(method_exists($cost,'getCostAmount'));

answered Aug 26, 2012 at 11:44

Romain

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