Some situations in PHP require a set of variables to have values depending on some condition. To achieve such `list()`

language construct.

For example, if `$a==1`

, then `$b=2; $c=2`

, else if `$a==2`

, then `$b=...`

etc. If the condition is the value of some variable, like `$a`

here, a switch-statement would look like:

1 2 3 4 5 6 7 8 9 10 11 12 13 | switch($a) { case 1: $b = 2; $c = 2; break; case 2: $b = 4; $c = 3; // etc... default: $b = 9; $c = 9; } |

The number of lines required to express this grows explosively with the number of variables and conditions to set. Instead, use this more elegant way, based on list():

1 2 3 4 5 | list($b, $c) = [ 1 => [2, 2], 2 => [4, 3], // .. etc ][$a] ?? [9, 9] |

Which grows linearly in LoCs with the number of conditions. Other benefits are improved DRY-ness and the guarantee that all variables `list()`

A simple back of the envelope test with 5 variables and 10 conditions shows the following results. All code was properly indented and formatted. Note also how compressing the list-based approach results in a bigger compression which indicates more DRY-ness. For the sake of testing, a compacted switch-based form, without line-breaks or tabs after assignment is used too.

characters | lines | gzip % | |

switch-based | 723 | 71 | 30% |

switch-based (compacted) | 667 | 31 | 32% |

list-based | 302 | 11 | 58% |

These tests were `wc`

`gzip`

1 2 3 4 5 6 7 8 9 10 11 | list($a, $b, $c, $d, $e) = [ 1 => [ 1, 2, 3, 4, 5] 2 => [ 6, 7, 8, 9, 10] 3 => [11, 12, 13, 14, 15] 4 => [16, 17, 18, 19, 20] 5 => [21, 22, 23, 24, 25] 6 => [26, 27, 28, 29, 30] 7 => [31, 32, 33, 34, 35] 8 => [36, 37, 38, 39, 40] 9 => [41, 42, 43, 44, 45] ][$x] ?? [46, 47, 48, 49, 50]; |

The switch-based compact version is as follows:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | switch($x) { case 1: $a = 1; $b = 2; $c = 3; $d = 4; $e = 5; break; case 2: $a = 6; $b = 7; $c = 8; $d = 9; $e = 10; break; case 3: $a = 11; $b = 12; $c = 13; $d = 14; $e = 15; break; case 4: $a = 16; $b = 17; $c = 18; $d = 19; $e = 20; break; case 5: $a = 21; $b = 22; $c = 23; $d = 24; $e = 25; break; case 6: $a = 26; $b = 27; $c = 28; $d = 29; $e = 30; break; case 7: $a = 31; $b = 32; $c = 33; $d = 34; $e = 35; break; case 8: $a = 36; $b = 37; $c = 38; $d = 39; $e = 40; break; case 9: $a = 41; $b = 42; $c = 43; $d = 44; $e = 45; break; default: $a = 46; $b = 47; $c = 48; $d = 49; $e = 50; } |

Check out the one-liner to pick random values from an array.

In PHP 7.3, you can use array-destructuring to get rid of the `list()`

language construct. E.g.: `[$a, $b] = [1, 2];`