Is there a PHP function for swapping the values of two variables?

Question

Say for instance I have ...

$var1 = \"ABC\"
$var2 = 123

and under certain conditions I want to sw

Answer 1

<?php

swap(50, 100);

function swap($a, $b) 
{
   $a = $a+$b;
   $b = $a - $b;
   $a = $a - $b;
   echo "A:". $a;
   echo "B:". $b;
 }
?>

Answer 2

For numbers:

$a = $a+$b;
$b = $a-$b;
$a = $a-$b;

Working:

Let $a = 10, $b = 20.

$a = $a+$b (now, $a = 30, $b = 20)

$b = $a-$b (now, $a = 30, $b = 10)

$a = $a-$b (now, $a = 20, $b = 10 SWAPPED!)

Answer 3

If both variables are integers you can use mathematical approach:

$a = 7; $b = 10; $a = $a + $b; $b = $a - $b; $a = $a - $b;

Good blog post - http://booleandreams.wordpress.com/2008/07/30/how-to-swap-values-of-two-variables-without-using-a-third-variable/

Answer 4

It is also possible to use the old XOR trick ( However it works only correctly for integers, and it doesn't make code easier to read.. )

$a ^= $b ^= $a ^= $b;

Answer 5

TL;DR

There isn't a built-in function. Use swap3() as mentioned below.

Summary

As many mentioned, there are multiple ways to do this, most noticable are these 4 methods:

function swap1(&$x, &$y) {
    // Warning: works correctly with numbers ONLY!
    $x ^= $y ^= $x ^= $y;
}
function swap2(&$x, &$y) {
    list($x,$y) = array($y, $x);
}
function swap3(&$x, &$y) {
    $tmp=$x;
    $x=$y;
    $y=$tmp;
}
function swap4(&$x, &$y) {
    extract(array('x' => $y, 'y' => $x));
}

I tested the 4 methods under a for-loop of 1000 iterations, to find the fastest of them:

• swap1() = scored approximate average of 0.19 seconds.
• swap2() = scored approximate average of 0.42 seconds.
• swap3() = scored approximate average of 0.16 seconds. Winner!
• swap4() = scored approximate average of 0.73 seconds.

And for readability, I find swap3() is better than the other functions.

Note

• swap2() and swap4() are always slower than the other ones because of the function call.
• swap1() and swap3() both performance speed are very similar, but most of the time swap3() is slightly faster.
• Warning: swap1() works only with numbers!

Answer 6

Another way:

$a = $b + $a - ($b = $a);