PHP 7.3: Warning on undefined variable names passed to
compact function, that is used to create an array from a given list of variable names, now emits a PHP notice if it encounters an undefined variable.
Prior to PHP 7.3, undefined variables were simply ignored:
From PHP 7.3 and later,
compact function emits a PHP notice when it encounters an undefined variable:
Notice: compact(): Undefined variable: foo in ... on line ... Notice: compact(): Undefined variable: bar ... on line ...