Php empty vs isset performance

Question

I’m cleaning up a lot of PHP code and always program with PHP error_reporting set to E_ALL and display_errors turned on so that I make sure to catch any PHP messages that come up. Since starting on this site, I have fixed literally hundreds (maybe thousands) of PHP Notices about using uninitialized variables and non-existent array indexes.

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I have been fixing problems like this where $somevar is sometimes undefined:

if ($somevar)

by changing it to:

if (isset($somevar) && $somevar)

This successfully gets rid of the NOTICEs, but adds some overhead because PHP has to perform two checks. After fixing a lot of this in this manner, I’ve noticed that the pages seem to be generated a little slower.

So, to provide some conclusive results to myself, I wrote up a quick benchmarking script – available at php_empty_benchmark.php. It goes through 1,000,000 tests using each of these methods:

if ($a) – This generates a notice if $a is not set
if (isset($a)) – A simple clean way to check if the variable is set (note that it is not equivalent to the one above)
if (isset($a) && ($a) – The one that I have been using which is equivalent to if($a), but doesn’t generate a notice.
if (!empty($a)) – This is functionally equivalent to if($a), but doesn’t generate a notice.

It measures the time to perform 1 million tests using a defined percentage of values that are set.Â It then computes the difference as a percentage of the time taken for the original test (the one that generates the notices).Â Â A ‘diff’ of 100 means that the execution time is the same, greater than 100 means that it is faster, and less than 100 means that it is slower. A typical test produced these results:

    With NOTICE: 0.19779300689697
    With isset:  0.19768500328064 / Diff: 100.05463419811
    With both:   0.21704912185669 / Diff: 91.128222590815
    with !empty: 0.19779801368713 / Diff: 99.997468735875

In summary, using the if (isset($a) && $a) syntax is about 8-10% slower than generating the PHP Notice. Using !empty() should be a drop-in replacement that doesn’t generate the notice and has virtually no performance impact. Using ifset() also has no performance impact, but is not exactly the same as ‘if($a)’ since isset() will return true if the variable is set to a false value. I included it here, because it often make the code a little more readable than the !empty($a) syntax. For example:

$myvalue = !empty($_REQUEST['myvalue']) ? $_REQUEST['myvalue'] : '';

Versus

$myvalue = isset($_REQUEST['myvalue']) ? $_REQUEST['myvalue'] : '';

I'm aware of the benchmarks for isset() vs empty(), but I have code I need to execute only when the argument is null. This is in a function that executes many times so I'd like to optimize it.

I know that isset() is faster than empty(), but what about !isset() vs. === null? I know that the variable will exist, so I only need to test it against null.

I'm thinking of the possible penalty for the ! operator.

asked Jul 2, 2017 at 6:11

I felt lazy asking someone else to benchmark this, so I tried a million iterations.

The difference is trivial, so !isset() is a better option since === null would throw an error if the variable was ever undefined.

One Million iterations:

   !isset()  .1118
   === null  .1046

BTW, there is an (also trivial) penalty for the ! operator.

   isset()  .1118
   !isset() .1203

answered Jul 2, 2017 at 6:21

Bob RayBob Ray

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It's a known flaw in PHP that functions in standard library are inconsistent. Some of them have a terrible API that may return anything from object to null and false. Some of them take arguments by reference, like for instance array sorting functions do. In short there's quite a bit features that work in a complicated fashion that makes the code worse.

A part of being a good programmer is to identify features in the language that hurt the code, the software we're building. Once those things are identified, a good programmer will minimize the impact of using those features or completely avoid using them if possible.

So, i've been stumbling lately quite a lot on isset and empty functions. These functions tap really well in to the weakly typed and procedural side of PHP. If you've already been riding the wave of modern PHP for a while, you've learned to hate that side of PHP.

isset

isset function in PHP docs:

isset — Determine if a variable is declared and is different than NULL"

And by example:

php > var_dump(isset($foo));
bool(false)

php > $foo = 'bar';
php > var_dump(isset($foo));
bool(true)

php > $foo = null;
php > var_dump(isset($foo));
bool(false)

php > $list = ['foo' => 'bar'];
php > var_dump(isset($list['baz']));
bool(false)

php > var_dump(isset($list['foo']));
bool(true)

Looking at the definition in PHP docs we can see that the function does two things.

Determine if variable is declared
Determine if variable is different than null

On the example there's three usages that i've witnessed as use cases for isset. Null checking and testing that variable is declared, but also checking if array has a key. First two match the definition in PHP docs and the third is just something developers have started using.

Now, the thing why using isset should be avoided is exactly the thing it promises. It does two things. This causes confusion to the reader.

We don't know if a variable is declared? How did this happen?

Either we are doing something very clever, which as we know is an awful habit, or we are working with a completely procedural legacy system.

If we do know that the variable is declared, then the only reason we'd use isset is for null checking. And for that, i'd recommend explicit null checks. In this code you obviously see easily where $customer came without any mutations. IRL there could be a lot more logic between these statements.

$customer = Customer::find($customerId);
if ($customer === null) {
    // throw
}

An alternative using the same solution that would be even more explicit and clear to the reader would be to null check with instanceof. In this case we know exactly what we're dealing with when we work with $customer.

$customer = Customer::find($customerId);
if (!$customer instanceof Customer) {
    // throw
}

Third situation i've seen, and personally used quite a lot, is checking if an array has a specific key:

if (isset($payload['username'])) {}

This is also another case where there's already a more explicit way to handle the problem.

if (array_key_exists('username', $payload')) {}

I admit, using isset is not the most serious offense. But it still is usually used for either null checking or testing if variable is declared, almost never for both. Being more explicit in these cases will help readers of your code.

empty

empty function in PHP docs:

Returns FALSE if var exists and has a non-empty, non-zero value. Otherwise returns TRUE.
The following values are considered to be empty:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)

Wow, so i might be dealing with a string, integer, float, boolean, null or an array. If isset was bad for doing two things, empty is a completely different beast. It does seven things! It answers to seven different questions.

First step to resolve the problem is to use type hints everywhere. Use argument type hints and return type hints in every method and function you write. NOTE: This applies to those developers who work with PHP7 or higher.

Second step is to use more explicit conditionals. This means that the readers of the code don't have to dig deep to boring details when trying to understand what you're trying to accomplish. Using strict comparison (===) is very important.

if (strlen($foo) === 0) {} // Clearly a string
if ($foo === 0) {} // Clearly a number
if ((int) $foo === 0) {} // Clearly expected to be treated as a number
if ($foo === false) {} // Clearly a boolean
if (count($foo) === 0) {} // Clearly an array
if ($foo === null) {} // Clearly null or something useful

As a side note, using return type hints is a very good practice. It will result to more clear interfaces. Once you have a return type hint in place, there's no way you can return multiple different things from your method (assuming you don't use nullable type hints, as you should not).

Are you ready to throw isset() and empty() in to history's trash bin? Tell me what you think!

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