Memory efficient array permutation in PHP 5.5 using generators
Generators support was introduced in PHP 5.5. The yield keyword is a really cool thing that allows to write an elegant and memory efficient code. It was existing in another dynamic languages like python for quite a long time and now it is in PHP as well! To demonstrate generators concept, i wrote a sample function that yields all permutations of the given array and avoids of data copying on recursive calls: function permute( $array ) { $length = sizeof( $array ); $inner = function ( $ix = []) use ( $array , $length , & $inner ) { $yield = sizeof( $ix ) == $length - 1 ; for ( $i = 0 ; $i < $length ; $i ++) { if (in_array( $i , $ix )) { continue ; } elseif ( $yield ) { $toYield = []; foreach (array_merge( $ix , [ $i ]) as $index ) { $toYield [] = $array [ $index ]; } yield $toYield ; } el