The data

$newSong = array ( 'band' => 'new edition', 'title' => 'you are not my kind of girl', )
$oldSong = array ( 'band' => 'new edition', 'title' => 'Mr Telephone Man', 'year' => '1984', )

The results

Test	Result
`array_merge($newSong, $oldSong)`	`array ( 'band' => 'new edition', 'title' => 'Mr Telephone Man', 'year' => '1984', )`
`array_replace($newSong, $oldSong)`	`array ( 'band' => 'new edition', 'title' => 'Mr Telephone Man', 'year' => '1984', )`
`$newSong + $oldSong`	`array ( 'band' => 'new edition', 'title' => 'you are not my kind of girl', 'year' => '1984', )`
`array_merge($oldSong, $newSong)`	`array ( 'band' => 'new edition', 'title' => 'you are not my kind of girl', 'year' => '1984', )`
`array_replace($oldSong, $newSong)`	`array ( 'band' => 'new edition', 'title' => 'you are not my kind of girl', 'year' => '1984', )`
`$oldSong + $newSong`	`array ( 'band' => 'new edition', 'title' => 'Mr Telephone Man', 'year' => '1984', )`