PHP 5.4 arrived on 1 March with [] as a literal array, and because it looks like a formatting preference it turns up in changes as though it were one. It is not a style question: on 5.3 it is a parse error, and a parse error takes the whole file rather than the statement, so a helper included on every request fatals the entire application.
// parses on 5.3 and on 5.4
$filters = array('brand_id' => 17, 'in_stock' => true);
// 5.4 only. On 5.3 the file never compiles:
// PHP Parse error: syntax error, unexpected '[' in Catalogue.php on line 12
$filters = ['brand_id' => 17, 'in_stock' => true];
// so lint against the oldest binary you deploy to, not the newest one installed
// find . -name '*.php' -print0 | xargs -0 -n1 /usr/bin/php5.3 -lThe deciding factor is the deployment target, not the diff. Shared hosting is overwhelmingly still 5.3 and will be for a while, and an application that has to run on both cannot use the short form at all — there is no conditional, no polyfill and no graceful degradation available for syntax. What it buys, honestly, is five characters and a slightly quieter nested array; that is worth having once the whole estate is on 5.4 and worth nothing before then. If the codebase is going to adopt it, adopt it in one change with a version bump in composer.json and a php -l pass over the tree using the oldest interpreter in play, rather than letting it arrive one file at a time.