In MediaWiki core's includes/registration/ directory, there are a few (two I think) places we use array_map for very simple operations:
$this->globals["wgExtensionMessagesFiles"] += array_map( function ( $file ) use ( $dir ) { return "$dir/$file"; }, $info['ExtensionMessagesFiles'] );
Since these are quick operations, we can make this code faster by using a foreach loop instead of array_map with a closure (unnecessary function calls are expensive).
- https://secure.php.net/manual/en/function.array-map.php
- https://secure.php.net/manual/en/control-structures.foreach.php
I'll mentor this task for Google-Code-in-2017 .