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<?php $formatted = ['foo' => 'bar', 'foo10' => 'bar10']; $formatted = array_change_key_case($formatted, CASE_UPPER); var_dump($formatted);
based on XV73M
Output for 5.6.0 - 5.6.30, hhvm-3.15.4, 7.0.0 - 7.3.0rc3
array(2) { ["FOO"]=> string(3) "bar" ["FOO10"]=> string(5) "bar10" }