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<?php // Surprise surprise! When the 2nd array param of array_diff() contains an elemant with value false, // the result will no longer contain null values. function myIsset($value) { return isset($value); } $arrayWithTrueValue = array( 'null1' => null, 'null2' => null, 'bool' => true, ); $filteredArray = array_filter($arrayWithTrueValue, 'myIsset'); echo "$arrayWithTrueValue has three elements..\n"; var_dump($arrayWithTrueValue); echo "$filteredArray has one element (only isset(true) === true)\n"; var_dump($filteredArray); echo "so the difference is an array with two elements..\n"; var_dump(array_diff($arrayWithTrueValue, $filteredArray)); $arrayWithFalseValue = $arrayWithTrueValue; $arrayWithFalseValue['bool'] = false; $filteredArrayWithOnlyFalse = array_filter($arrayWithFalseValue, 'myIsset'); var_dump($arrayWithFalseValue, $filteredArrayWithOnlyFalse, array_diff($arrayWithFalseValue, $filteredArrayWithOnlyFalse));
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
Warning: Array to string conversion in /in/MO7j4 on line 19 Array has three elements.. array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(true) } Warning: Array to string conversion in /in/MO7j4 on line 22 Array has one element (only isset(true) === true) array(1) { ["bool"]=> bool(true) } so the difference is an array with two elements.. array(2) { ["null1"]=> NULL ["null2"]=> NULL } array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(false) } array(1) { ["bool"]=> bool(false) } array(0) { }
Output for 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.31, 7.4.0 - 7.4.33
Notice: Array to string conversion in /in/MO7j4 on line 19 Array has three elements.. array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(true) } Notice: Array to string conversion in /in/MO7j4 on line 22 Array has one element (only isset(true) === true) array(1) { ["bool"]=> bool(true) } so the difference is an array with two elements.. array(2) { ["null1"]=> NULL ["null2"]=> NULL } array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(false) } array(1) { ["bool"]=> bool(false) } array(0) { }
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 7.3.32 - 7.3.33
Array has three elements.. array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(true) } Array has one element (only isset(true) === true) array(1) { ["bool"]=> bool(true) } so the difference is an array with two elements.. array(2) { ["null1"]=> NULL ["null2"]=> NULL } array(3) { ["null1"]=> NULL ["null2"]=> NULL ["bool"]=> bool(false) } array(1) { ["bool"]=> bool(false) } array(0) { }

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