Which is faster? Constants, Variables or Variable Arrays

My current web application uses about 30 or so Contants (DEFINE()). I am reading things that variables are quicker. Provided that there is a naming convention to avoid variable overwrites, the only other draw back I see is that these variables would have to be defined as global variables some how in every function.

Which is faster? I use these constants a whole lot throughout my application and will probably be forever adding more to the list and they are used in and out of functions and classes.

Constants defined using define() are fairly slow in PHP. People actually wrote extensions (like hidef) to improve the performance.

But unless you have loads of constants this shouldn't make much of a difference.

As of PHP 5.3 you can also use compile-time constants using const NAME = VALUE;. Those are much faster.

The difference would be really small (micro optimizations). You would better encapsulate some of your constants in classes so you can access them by Classname::CONSTANT to not pollute the global namespace of your application.

A quick test showed that defining constants (define('FOO', 'bar');) is about 16 to 18 times slower than defining a variable ($foo = 'bar';), but using the defined (constant) value is about 4 to 6 times faster.

I was benchmarking constants vs variables and noticed a significant improvement of performance when using variables over constants. I know it is pretty obvious but it is definietely worth taking into the cosideration that use of local variables over constants whenever possible.

If constants are being used inside loops number of times, it is definitely worth declaring the constant as a class / local variable and use it instead.

The benchmarking test case includes creating two functions. Each has a loop that executes 10000000 times. One access a constant declared in a constant file and one access a local variable.

TestConstants.php

class TestConstants 
{   
    const TEST_CONSTANT = 'This is a constant value';

}

Test.php

use TestConstants;

class Test {

    protected $TEST_CONSTANT;
    protected $limit = 10000000;
    function __construct() {
        $this->TEST_CONSTANT = 'This is a constant value';
    }

    function testA() {
        $limit = $this->limit;
        $time_start = microtime(true); 
        for ($i = 0; $i < $limit; ++$i) {
            TestConstants::TEST_CONSTANT;
        }
        $time_end = microtime(true);
        $execution_time = ($time_end - $time_start);
        echo ''. $execution_time .' seconds <br/>';
    }

    function testB() {
        $limit = $this->limit;
        $time_start = microtime(true); 
        for ($i = 0; $i < $limit; ++$i) {
            $this->TEST_CONSTANT;
        }
        $time_end = microtime(true);
        $execution_time = ($time_end - $time_start);
        echo ''. $execution_time .' seconds <br/>';
    }   
}

$test = new Test();
$test->testA();
$test->testB();

Results are as follows

testA() executes in 0.55921387672424 seconds

and

testB() executes in 0.33076691627502 seconds

PHP Version

5.6.30

I thought to share this as someone out there might be benefitted by avoiding direct calls to constants (especially inside loops) by declaring them as variables wherever applicable.

Thank you.