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1616

answers:

13

I'm pretty sure the answer to this question is no, but in case there's some PHP guru

is it possible to write a function in a way where invalid arguments or non existent variables can be passed in and php will not error without the use of '@'

Much like empty and isset do. You can pass in a variable you just made up and it won't error.

ex:

empty($someBogusVar); // no error

myHappyFunction($someBogusVar); // Php warning / notice

+1  A: 

No, because this isn't really anything to do with the function; the error is coming from attempting to de-reference a non-existent array key. You can change the warning level of your PHP setup to surpress these errors, but you're better off just not doing this.

Having said that, you could do something like

function safeLookup($array, $key)
{
  if (isset($array, $key))
    return $array[$key];

  return 0;
}

And use it in place of array key lookup

defaultValue(safeLookup($foo, "bar"), "baz);

Now I need to take a shower :)

Adam Wright
A: 

@Brian: I use a trinary operation to do the check for me:

return $value ? $value : $default;

this returns either $value OR $default. Depending upon the value of $value. If it is 0, false, empty or anything similar the value in $default will be returned.

I'm more going for the challenge to emulate functions like empty() and isset()

SeanDowney
A: 

And going further up the abstraction tree, what are you using this for?

You could either initialize those values in each class as appropriate or create a specific class containing all the default values and attributes, like:

class Configuration {

    private var $configValues = array( 'cool' => 'Defaultcoolval' ,
                                       'uncool' => 'Defuncoolval'  );

    public setCool($val) {
        $this->configValues['cool'] = $val;
    }

    public getCool() {
        return $this->configValues['cool'];
    }

}

The idea being that, when using defaultValue function everywhere up and down in your code, it will become a maintenance nightmare whenever you have to change a value, looking for all the places where you've put a defaultValue call. And it'll also probably lead you to repeat yourself, violating DRY.

Whereas this is a single place to store all those default values. You might be tempted to avoid creating those setters and getters, but they also help in maintenance, in case it becomse pertinent to do some modification of outputs or validation of inputs.

Vinko Vrsalovic
A: 

I'm sure there could be a great discussion on ternary operators vrs function calls. But the point of this question was to see if we can create a function that won't throw an error if a non existent value is passed in without using the '@'

SeanDowney
+2  A: 

You can do this using func_get_args like so:

error_reporting(E_ALL);
ini_set('display_errors', 1);

function defaultValue() {
    $args = func_get_args();

    foreach($args as $arg) {
        if (!is_array($arg)) {
            $arg = array($arg);
        }
        foreach($arg as $a) {
            if(!empty($a)) {
                return $a;
            }
        }
    }

    return false;
}

$var = 'bob';

echo defaultValue(compact('var'), 'alpha') . "\n"; //returns 'bob'
echo defaultValue(compact('var2'), 'alpha') . "\n"; //returns 'alpha'
echo defaultValue('alpha') . "\n"; //return
echo defaultValue() . "\n";

This func goes one step further and would give you the first non empty value of any number of args (you could always force it to only take up to two args but this look more useful to me like this).

EDIT: original version didn't use compact to try and make an array of args and STILL gave an error. Error reporting bumped up a notch and this new version with compact is a little less tidy, but still does the same thing and allows you to provide a default value for non existent vars.

reefnet_alex
i still get a undefined error:Notice: Undefined variable: var2 in file.php on line 19
SeanDowney
buggeration - you're right :) OK this version fixes it. You have to use compact to extract the variables from out of the mix (including any fantasy ones which don't exist) but should still allow for some compact code (no pun intended)
reefnet_alex
that's a clever usage of the compact function. I've never seen that in such a use, thanks for the tip.
SeanDowney
A: 

@Sean That was already answered by Brian

return isset($input) ? $input : $default;
Vinko Vrsalovic
but within the function the error will have already fired yes?
SeanDowney
A: 

Sean, you could do:

$result = ($func_result = doLargeIntenseFunction()) ? $func_result : 'no result';

EDIT:

I'm sure there could be a great discussion on ternary operators vrs function calls. But the point of this question was to see if we can create a function that won't throw an error if a non existent value is passed in without using the '@'

And I told you, check it with isset(). A ternary conditional's first part doesn't check null or not null, it checks true or false. If you try to check true or false on a null value in PHP, you get these warnings. isset() checks whether a variable or expression returns a null value or not, and it returns a boolean, which can be evaluated by the first part of your ternary without any errors.

Brian Warshaw
+7  A: 

Summing up, the proper answer is no, you shouldn't (see caveat below).

There are workarounds already mentioned by many people in this thread, like using reference variables or isset() or empty() in conditions and suppressing notices in PHP configuration. That in addition to the obvious workaround, using @, which you don't want.

Summarizing an interesting comment discussion with Gerry: Passing the variable by reference is indeed valid if you check for the value of the variable inside the function and handle undefined or null cases properly. Just don't use reference passing as a way of shutting PHP up (this is where my original shouldn't points to).

Vinko Vrsalovic
You're statement in bold is incorrect, please take a look at porneL's answer: http://stackoverflow.com/questions/55060/884770#answer-311954
Gerry
His statement in bold is *not* incorrect. If you've designed your functions so that you need to suppress warnings/errors caused by missing arguments, then you designed your functions wrong and need to start over. porneL's answer is a valid workaround, but it's not a good idea.
dirtside
I just edited my answer to correct the incorrect bold statement, I wasn't aware of the by reference trick.
Vinko Vrsalovic
It said "no you can't". It seems Vinko agrees that the statement was incorrect and has modified it, which I thank him for. It is not suppressing an error either. In the case of an undefined variable being used as an argument, it is creating a null reference, which can then be tested inside of myHappyFunction() to see if it in fact exists. I still don't agree with how this has been rewritten. You definitely should not use this technique to suppress errors, but it does have valid applications, such as the creation of an alternative empty() function as was asked for in the question!
Gerry
The question didn't ask for the creation of an alternative empty() function, only for the creation of a function with empty()-like behavior with respect to undefined variables, for which the usage was not specified. I still stand by that you shouldn't. I don't think there's a need to qualify most shouldn'ts by all the possible exceptions, which always exist. If you know what you are doing you certainly can do what you should not without any harmful side effect.
Vinko Vrsalovic
Ok well I think it's only a should not if used in a bad way. As I said, it's only creating a reference to NULL, which by itself I believe is not a "should not" and it's unlikely this would have been an oversight by the PHP devs. It's the misuse of this to hide errors (which is probably how most would use it if they knew) that is a "should not". But I'm happy to agree to disagree on this. Our comments are both there so people can read them and decide for themselves. I like the revised version of your answer a lot better anyway. It says good things about you that you came back and fixed it.
Gerry
The main point you are overlooking is that the question explicitly states "... a way where invalid arguments or non existent variables can be passed in and php will not error without the use of '@'." This points to the intended usage which is where we agree on "shouldn't."
Vinko Vrsalovic
Yes and if I wanted to emulate empty(), that is exactly what I would want. Because I would want to check for the validity of the variable inside of the function without triggering an error in the same way an error is not thrown when you call the official empty(). But that doesn't mean your suppressing an error, but instead coding it in a way that will not cause an error, which is what porneL's function does.
Gerry
This is assuming you indeed check for the value of the variable inside the function. Doing so demonstrates that "you know what you are doing".
Vinko Vrsalovic
+3  A: 

You don't get any error when variable is passed by reference (PHP will create new variable silently):

 function myHappyFunction(&$var)
 {       
 }

But I recommend against abusing this for hiding programming errors.

porneL
A: 

While the answer to the original question is "no", there is an options no one has mentioned.

When you use the @ sign, all PHP is doing is overriding the error_reporting level and temporarily setting it to zero. You can use "ini_restore('error_reporting');" to set it back to whatever it was before the @ was used.

This was useful to me in the situation where I wanted to write a convenience function to check and see if a variable was set, and had some other properties as well, otherwise, return a default value. But, sending an unset variable through caused a PHP notice, so I used the @ to suppress that, but then set error_reporting back to the original value inside the function.

Something like:

$var = @foo($bar);

function foo($test_var)
{
     ini_restore('error_reporting');

     if(is_set($test_var) && strlen($test_var))
     {
          return $test_var;
     }
     else
     {
          return -1;
     }
}

So, in the case above, if $bar is not set, I won't get an error when I call foo() with a non-existent variable. However, I will get an error from within the function where I mistakenly typed is_set instead of isset.

This could be a useful option covering what the original question was asking in spirit, if not in actual fact.

+1  A: 

is it possible to write a function in a way where invalid arguments or non existent variables can be passed in and php will not error without the use of '@'

Yes you can!

porneL is correct [edit:I don't have enough points to link to his answer or vote it up, but it's on this page]

He is also correct when he cautions "But I recommend against abusing this for hiding programming errors." however error suppression via the Error Control Operator (@) should also be avoided for this same reason.

I'm new to Stack Overflow, but I hope it's not common for an incorrect answer to be ranked the highest on a page while the correct answer receives no votes. :(

Gerry
I now have enough points to link straight to porneL's answer: http://stackoverflow.com/questions/55060/884770#answer-311954 It's good to see that over time things start to turn around on a stackoverflow thread, with points eventually being appropriated to the correct person. :) It's just a shame that this thread has already been viewed 753 times and of thos people probably missed porneL's post (which was right at the bottom with zero votes) and instead saw the incorrect answer.
Gerry
A: 

If you simply add a default value to the parameter, you can skip it when calling the function. For example:

function empty($paramName = ""){
    if(isset($paramName){
        //Code here
    }
    else if(empty($paramName)){
        //Code here
    }
}
BraedenP
+1  A: 

There are valid cases where checking becomes cumbersome and unnessesary.
Therfore i've written this little magic function:

/**
 * Shortcut for getting a value from a possibly unset variable.
 * Normal:
 *   if (isset($_GET['foo']) && $_GET['foo'] == 'bar') {
 * Short:
 *   if (value($_GET['foo']) == 'bar') {
 *
 * @param mixed  $variable 
 * @return mixed  Returns null if not set
 */
function value(&$variable) {
    if (isset($variable)) {
     return $variable;
    }
}

It doesn't require any changes to myHappyFunction().
You'll have to change

myHappyFunction($someBogusVar);

to

myHappyFunction(value($someBogusVar));

Stating your intent explicitly. which makes it good practice in my book.

Bob Fanger