trying to merge arrays in various ways

array_merges.php

<?php

function my_merge( $a, $d ) {
  foreach ( $d as $name => $default ) {
    if ( array_key_exists( $name, $a ) && !is_null($a[ $name ]) ) {
        $out[ $name ] = $a[ $name ];
    } else {
        $out[ $name ] = $default;
    }
  }
  return $out;
}

$defaults = [
  'a'=>'apple',
  'b'=>'banana',
  'c'=>'carrot',
];

$options = [
  'a'=>null,
  'b'=>'bowling ball',
  'c'=>'cucumber'
];

// array_merge is not enough
$m1 = array_merge( $options, $defaults );
// this way works, but is weird to read, and moves keys around
$m2 = array_filter($options) + array_filter($defaults);
// this way works, and is readable
$m3 = my_merge( $options, $defaults );

var_dump($m1);
var_dump($m2);
var_dump($m3);