連想配列の定数を + で結合してみた

<?php

const ARR1 = ['apple' =>1, 'buleberry' =>1, 'pear'=>1 ];
const ARR2 = ['egg' => 1, 'milk' => 1, 'cheese' =>1 ];
const ARR3 = ['cabbage' => 1, 'onion' => 1, 'roquette' =>1 ];

$arr = ARR1 + ARR2 + ARR3;
print_r($arr);
Array
(
    [apple] => 1
    [buleberry] => 1
    [pear] => 1
    [egg] => 1
    [milk] => 1
    [cheese] => 1
    [cabbage] => 1
    [onion] => 1
    [roquette] => 1
)