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Array unpacking in PHP

A neat trick for extracting information from arrays into variables.

One of PHP’s less known language constructs is list(), very useful for unpacking indexed arrays. Consider the following simple example denoting its usage:

$record = ['me', '1.800.123.4567', ''];

// Unpack the array into variables, skipping the phone number
list($name, , $email) = $record;

This clean, readable, scalable approach is great for processing data records, unpacking an SQL result row, etc.

Maps / Associative Arrays

As of PHP 7.1.0 list() can now also contain explicit keys, which can be given as arbitrary expressions. Mixing of integer and string keys is allowed; however, elements with and without keys cannot be mixed.

$record = [1, 2, 3, 4, 'a' => '5'];

// Unpack index 1, 3, and 'a' into variables
list(1 => $key1, 'a' => $keya, 3 => $key3) = $record;

Unpacking Maps / Associative Arrays PHP < 7.1.0

There are options: extract() unpacks associative arrays into variables matching the names of their respective keys.

There are both runtime and security issues to consider when using extract() – you will find both discussed in the PHP documentation for the function.

Reasons to favour list() over extract()

  • You have control over which indices are extracted
  • You have control over the naming of the variables
  • list() is a language construct and will be very fast