I'm trying to combine isset and is_null in one function for ease of use
My approach:
class sys {
public static function is_null(&$variable) {
// if it's not set
if (!isset($variable)) {
return true;
}
// if array
if (is_array($variable)) {
return (boolean) (count($variable) < 1);
}
// if string
return (boolean) (strlen($variable) < 1);
}
}
The problem I'm having when i use it within an object is following exception:
ErrorException [ Notice ]: Indirect modification of overloaded property xxx has no effect.
For ease of use? The equivalent is return !isset($var) || empty($var);. is that so hard?
The thing that you need to realize when building a function like this, is that isset() is not a function. It's a language construct. So you can't pass a variable to a function, and then call isset on that variable (well, without generating a notice at least).
Secondly, there's no need to cast to boolean in :return (boolean) (strlen($variable) < 1);. It's exactly the same as return strlen($variable) < 1;.
Third, there's no reason to count() or use strlen(), since that's exactly what empty() was designed to check for.
Fourth, there's no reason at all to pass the argument by reference. It won't change anything, and it's needlessly creating references where there's no reason to. Just take the argument as normal (it won't use any more memory thanks to copy-on-write).
All in all, I would suggest not making this sort of "helper" function. Just use !isset($var) || empty($var) if you want to check if it's empty. It's clearer, makes more semantic sense, and frankly isn't duplicating effort. And if you don't care about the notice, you can just replace the entire call with if (empty($variable))...
But if you do use this kind of function, I'd suggest changing the name. It will return true even if the variable is not null, so calling the function is_null is down right misleading. Perhaps is_empty would be better...
just use empty()
Related
I would think the following piece of code should work, but it doesn't (Edited: Now works in PHP 5.5+):
if (!empty($r->getError()))
Where getError() is simply:
public function getError()
{
return $this->error;
}
Yet I end up with this error:
can't use method return value in write context
What does this mean? Isn't this just a read?
empty() needs to access the value by reference (in order to check whether that reference points to something that exists), and PHP before 5.5 didn't support references to temporary values returned from functions.
However, the real problem you have is that you use empty() at all, mistakenly believing that "empty" value is any different from "false".
Empty is just an alias for !isset($thing) || !$thing. When the thing you're checking always exists (in PHP results of function calls always exist), the empty() function is nothing but a negation operator.
PHP doesn't have concept of emptyness. Values that evaluate to false are empty, values that evaluate to true are non-empty. It's the same thing. This code:
$x = something();
if (empty($x)) …
and this:
$x = something();
if (!$x) …
has always the same result, in all cases, for all datatypes (because $x is defined empty() is redundant).
Return value from the method always exists (even if you don't have return statement, return value exists and contains null). Therefore:
if (!empty($r->getError()))
is logically equivalent to:
if ($r->getError())
Note: This is a very high voted answer with a high visibility, but please note that it promotes bad, unnecessary coding practices! See #Kornel's answer for the correct way.
Note #2: I endorse the suggestions to use #Kornel's answer. When I wrote this answer three years ago, I merely meant to explain the nature of the error, not necessarily endorse the alternative. The code snippet below is not recommended.
It's a limitation of empty() in PHP versions below 5.5.
Note: empty() only checks variables as
anything else will result in a parse
error. In other words, the following
will not work: empty(trim($name)).
You'd have to change to this
// Not recommended, just illustrates the issue
$err = $r->getError();
if (!empty($err))
Prior to PHP 5.5, the the PHP docs used to say:
empty() only checks variables as anything else will result in a parse error
In PHP < 5.5 you weren't able use empty() directly on a function's return value. Instead, you could assign the return from getError() to a variable and run empty() on the variable.
In PHP >= 5.5 this is no longer necessary.
I usually create a global function called is_empty() just to get around this issue
function is_empty($var)
{
return empty($var);
}
Then anywhere I would normally have used empty() I just use is_empty()
As pointed out by others, it's a (weird) limitation of empty().
For most purproses, doing this is equal as calling empty, but this works:
if ($r->getError() != '')
The issue is this, you want to know if the error is not empty.
public function getError() {
return $this->error;
}
Adding a method isErrorSet() will solve the problem.
public function isErrorSet() {
if (isset($this->error) && !empty($this->error)) {
return true;
} else {
return false;
}
}
Now this will work fine with this code with no notice.
if (!($x->isErrorSet())) {
echo $x->getError();
}
I'm not sure if this would be a common mistake, but if you do something like:
$var = 'value' .= 'value2';
this will also produce the same error
Can't use method return value in write context
You can't have an = and a .= in the same statement. You can use one or the other, but not both.
Note, I understand this is unrelated to the actual code in the question, however this question is the top result when searching for the error message, so I wanted to post it here for completeness.
The alternative way to check if an array is empty could be:
count($array)>0
It works for me without that error
I would think the following piece of code should work, but it doesn't (Edited: Now works in PHP 5.5+):
if (!empty($r->getError()))
Where getError() is simply:
public function getError()
{
return $this->error;
}
Yet I end up with this error:
can't use method return value in write context
What does this mean? Isn't this just a read?
empty() needs to access the value by reference (in order to check whether that reference points to something that exists), and PHP before 5.5 didn't support references to temporary values returned from functions.
However, the real problem you have is that you use empty() at all, mistakenly believing that "empty" value is any different from "false".
Empty is just an alias for !isset($thing) || !$thing. When the thing you're checking always exists (in PHP results of function calls always exist), the empty() function is nothing but a negation operator.
PHP doesn't have concept of emptyness. Values that evaluate to false are empty, values that evaluate to true are non-empty. It's the same thing. This code:
$x = something();
if (empty($x)) …
and this:
$x = something();
if (!$x) …
has always the same result, in all cases, for all datatypes (because $x is defined empty() is redundant).
Return value from the method always exists (even if you don't have return statement, return value exists and contains null). Therefore:
if (!empty($r->getError()))
is logically equivalent to:
if ($r->getError())
Note: This is a very high voted answer with a high visibility, but please note that it promotes bad, unnecessary coding practices! See #Kornel's answer for the correct way.
Note #2: I endorse the suggestions to use #Kornel's answer. When I wrote this answer three years ago, I merely meant to explain the nature of the error, not necessarily endorse the alternative. The code snippet below is not recommended.
It's a limitation of empty() in PHP versions below 5.5.
Note: empty() only checks variables as
anything else will result in a parse
error. In other words, the following
will not work: empty(trim($name)).
You'd have to change to this
// Not recommended, just illustrates the issue
$err = $r->getError();
if (!empty($err))
Prior to PHP 5.5, the the PHP docs used to say:
empty() only checks variables as anything else will result in a parse error
In PHP < 5.5 you weren't able use empty() directly on a function's return value. Instead, you could assign the return from getError() to a variable and run empty() on the variable.
In PHP >= 5.5 this is no longer necessary.
I usually create a global function called is_empty() just to get around this issue
function is_empty($var)
{
return empty($var);
}
Then anywhere I would normally have used empty() I just use is_empty()
As pointed out by others, it's a (weird) limitation of empty().
For most purproses, doing this is equal as calling empty, but this works:
if ($r->getError() != '')
The issue is this, you want to know if the error is not empty.
public function getError() {
return $this->error;
}
Adding a method isErrorSet() will solve the problem.
public function isErrorSet() {
if (isset($this->error) && !empty($this->error)) {
return true;
} else {
return false;
}
}
Now this will work fine with this code with no notice.
if (!($x->isErrorSet())) {
echo $x->getError();
}
I'm not sure if this would be a common mistake, but if you do something like:
$var = 'value' .= 'value2';
this will also produce the same error
Can't use method return value in write context
You can't have an = and a .= in the same statement. You can use one or the other, but not both.
Note, I understand this is unrelated to the actual code in the question, however this question is the top result when searching for the error message, so I wanted to post it here for completeness.
The alternative way to check if an array is empty could be:
count($array)>0
It works for me without that error
I am aware that some built-in php functions have mixed return type, such as strpos().
Is there some sort of a 'Best Practice' on returning values from a custom php function?
Take a look at this
function getSupportedCurrencies() {
// code here
}
The getSupportedCurrencies() expects an array of currencies to be returned.
But if there is no supported currencies, we can easily return false or null.
But semantically, we should return an empty array().
I understand that PHP variables are loosely typed allowing the program to be flexible.
But what benefits does a loosely typed function provide? Does it just only give
programmers an opportunity to write bad code? Please give an example wherein it is
needed to have mixed return type. Thanks.
There is no really way to be typesafe in PHP as you mean, no really security that returned value is of wrong type. You may want to look at some extra tool like HipHop compiler (or to some other language).
Personally, when working with functions which accept arrays. I'd prefer something like:
function GetCur ($Argument = array()){
$Errors = 0;
if (!is_array($Argument)){
// If is not an array then increment the errors
$Errors++;
}
if (empty($Argument)){
// If passed array is empty then increment
$Errors++;
}
if ($Errors >0){
// If errors are higher than 0, then return false
return false;
}
// Do other validations that you need your function to do
}
Then validate as so:
if (GetCur($Array) !== false){
// function has not returned false, so correct information has been passed
}else{
// Function has returned false, so incorrect information has been passed. So log/show a error
}
a simple comparison would be to look at the workings for Strpos which specifies:
Warning This function may return Boolean FALSE, but may also return a
non-Boolean value which evaluates to FALSE. Please read the section on
Booleans for more information. Use the === operator for testing the
return value of this function.
Please note, this is an example. There are more efficient ways to handle countless if statements within a function, which would also provide better readability if you are creating an API
Is there any way to implement isset() in a setter method? That is, have the setter method check if the variable exists? From what I can tell no, but hopefully someone can confirm that for me. In a nutshell, I'm looking to avoid having to do
if (isset($arr[0])) $foo->setId($arr[0])
and simply just do
$foo->setId($arr[0])
and somehow implement the isset() logic in the setter method. Thanks!
No, you not can subscript a missing array element and expect it to work. The subscript will be evaluated before being sent to the method. This means the subscript will fail before the method even receives the argument.
Example
$arr = array(0 => 'a', 1 => 'b', 2 => 'c');
If I do $foo->setId($arr[0]) then $foo->setId() will receive a as a string, and it will never know it was subscripted from an array (not does it want to know).
So a $foo->setId($arr[3]) would give an error...
Undefined offset
No.
You're only passing the value of $arr[0] to the setter method, not the $arr[0] variable. $foo::setId has no idea of the existence of $arr or $arr[0], all it gets to see is its value.
And that's a good thing for encapsulation! Imagine if every function would have to check if its parameters actually existed:
function setId($id) {
// $id is defined, it's required (has no default value),
// and yet I can't be sure it actually exists here...?
}
You'll have to check if the variable exists before passing its value to a function.
First, read #alex's answer. (Edit: Read #deceze's answer, too)
In order to mimic what you want you can pass the array and the index separately:
$foo->setId($arr, 0);
And change the setId() method's signature (or add a safeSetId()):
function safeSetId($array, $index) {
if (isset($array[$index])) {
$this->setId($array[$index]);
}
}
This is not very pretty, though :)
Isset is not a function: it's a language construct. Language constructs are allowed to do magic; user-defined functions cant.
There is no way to reimplement the isset logic without isset itself (without modifications to PHP's source code, at least). If you try to implement it inside a function, the argument you receive will be null if the variable doesn't exist and a E_NOTICE error will be raised before your function is even called.
While you can't achieve what you're looking to do for reasons already given, you could still make the code more terse for very little overhead.
If the setId() function can handle null or if it is simply setting a member variable (which will by default be initialized to null), you could write a simple utility function like this:
function getValue($array, $key, $default = null) {
return isset($array[$key]) ? $array[$key] : $default;
}
and then call your setter like so:
$foo->setId(getValue($arr,0));
Again, there are drawbacks due to increased overhead and potential errors if your setter method expects a non-null value but this could decrease the amount of code slightly.
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
You don't get any error when a variable is passed by reference (PHP will create a new variable silently):
function myHappyFunction(&$var)
{
}
But I recommend against abusing this for hiding programming errors.
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).
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;
}
$var = 'bob';
echo defaultValue(compact('var'), 'alpha') . "\n"; //returns 'bob'
echo defaultValue(compact('var2'), 'alpha') . "\n"; //returns 'alpha'
echo defaultValue('alpha') . "\n"; //return
echo defaultValue() . "\n";
This func goes one step further and would give you the first non empty value of any number of args (you could always force it to only take up to two args but this look more useful to me like this).
EDIT: original version didn't use compact to try and make an array of args and STILL gave an error. Error reporting bumped up a notch and this new version with compact is a little less tidy, but still does the same thing and allows you to provide a default value for non existent vars.
There are valid cases where checking becomes cumbersome and unnessesary.
Therfore i've written this little magic function:
/**
* Shortcut for getting a value from a possibly unset variable.
* Normal:
* if (isset($_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($someBogusVar));
Stating your intent explicitly. which makes it good practice in my book.
No, because this isn't really anything to do with the function; the error is coming from attempting to de-reference a non-existent array key. You can change the warning level of your PHP setup to surpress these errors, but you're better off just not doing this.
Having said that, you could do something like
function safeLookup($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 :)
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. :(
#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 $default will be returned.
I'm more going for the challenge to emulate functions like empty() and isset()
#Sean That was already answered by Brian
return isset($input) ? $input : $default;
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.
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 '#'
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 $bar is not set, I won't get an error when I call foo() with a non-existent variable. However, I will get an error from within the function where I mistakenly typed is_set instead of isset.
This could be a useful option covering what the original question was asking in spirit, if not in actual fact.
If you simply add a default value to the parameter, you can skip it when calling the function. For example:
function empty($paramName = ""){
if(isset($paramName){
//Code here
}
else if(empty($paramName)){
//Code here
}
}
With a single line, you can acomplish it: myHappyFunction($someBogusVar="");
I hope this is what you are looking for. If you read the php documentation, under default argument values, you can see that assigning a default value to an function's argument helps you prevent an error message when using functions.
In this example you can see the difference of using a default argument and it's advantages:
PHP code:
<?php
function test1($argument)
{
echo $argument;
echo "\n";
}
function test2($argument="")
{
echo $argument;
echo "\n";
}
test1();
test1("Hello");
test1($argument);
$argument = "Hello world";
test1($argument);
test2();
test2("Hello");
test2($argument);
$argument = "Hello world";
test2($argument);
?>
Output for test1() lines:
Warning: Missing argument 1 for test1() .
Hello.
.
Hello world.
Output for test2() lines:
.
Hello.
Hello world.
This can also be used in combination to isset() and other functions to accomplish what you want.
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.