CODEWITHSUNDEEP
php
Alexandre Demelas
Alexandre Demelas

Reputation: 4710

Why isset() is more efficient to test than '==='?

Summarized, I made a loop with a few iterations to check the efficiency of each test:

$iterations = 99999999;
$var = null;

isset comparasion

  if ( isset( $var ) )
  {

  }

'===' comparasion

  if ( $var === null )
  {

  }

And i have this log, in microseconds:

'isset()': 1.4792940616608
'===': 1.9428749084473

For me, this is a little curious. Why isset() function is faster than one comparison operator as ===?

Upvotes: 7

Views: 854

Answers (3)

Phil Lewis
Phil Lewis

Reputation: 61

I'm not sure I would call 100 million "a few iterations". You appear to have accumulated about a half-second difference, divide that by 100 million and you get a whopping 5 nanosecond difference per iteration if my math is correct. With the difference being so small it may simply come down to the fact that isset only has one operand in this context and === has two.

It's impossible to even discuss the Zend engine's implementation details of the two examples without specifying a specific PHP version; source code is a moving target. Even minute changes to the implementations are going to effect the results over that many passes. I would not be surprised if you found the opposite to be the case on some versions of PHP and/or in a different context.

isset itself is covered by three different op-codes in the VM depending upon the context:

"Simple" Compiled Variables like your example: ZEND_ISSET_ISEMPTY_VAR

Arrays: ZEND_ISSET_ISEMPTY_DIM_OBJ (requires 2 operands, the var and the index)

Object properties: ZEND_ISSET_ISEMPTY_PROP_OBJ (also 2 operands, var and prop name)

It's an interesting question for curiosity's sake but we're in hair splitting territory and it's probably not a real-world optimization strategy.

Upvotes: 0

zneak
zneak

Reputation: 138251

Isset is not a function: it is a language built-in. Using isset is faster than using a function.

The other thing is that isset is used all over the place, so it makes sense that it's been profiled to death, whereas === maybe hasn't received as much love.

Other than that, you'd have to dig in the PHP source with a profiler to see exactly what's going on.

Upvotes: 1

Oldskool
Oldskool

Reputation: 34877

The === comparison is a strict check, meaning that the two objects you're comparing have to be of the same type. When you break it down in plain English, it's actually not that weird that === needs some more time. Consider the parser to do this:

if (isset($var)) {
    // Do I have something called $var stored in memory?
    // Why yes, I do.. good, return true!
}

if ($var === null) {
    // Do I have something called $var stored in memory?
    // Why yes, I do.. good! But is it a NULL type?
    // Yes, it is! Good, return true!
}

As you can see, the === operator needs to do an additional check before it can determine if the variable matches the condition, so it's not that strange that it is a little bit slower.

Upvotes: 4

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