array_filter Flag will ignored when callable is null

[tinostief]

From manual page: https://php.net/function.array-filter

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If the callback parameter is set to null, the flag is ignored. I expect array_filter to use an empty check for the mode used on key, or value, or both. But the flag is ignored and each time only the value is checked for empty.

Example:

array_filter([''=>'2',0=>'3',0,5=>3,null,'',[]], null, ARRAY_FILTER_USE_BOTH); does not filter the elements where key or value are empty. Only the elements where value is empty are filtered.

I expected all elements where key or value are empty to be filtered.

and

array_filter([''=>'2',0=>'3',0,5=>3,null,'',[]], null, ARRAY_FILTER_USE_KEY); does not filter the elements where key is empty. Only the elements where value is empty are filtered.

I had expected that all elements whose keys are empty would be filtered.

[aarkaynegi]

If my understanding is incorrect, please let me know

When you use array_filter with the "ARRAY_FILTER_USE_BOTH" flag, the callback function will receive both the key and the value of each element in the array

However, if the callback parameter is set to null, the default behavior is to remove any elements from the array where the value is considered "falsey" (i.e. an empty string, 0, null, or false)

Similarly, when you use array_filter with the "ARRAY_FILTER_USE_KEY" flag, the callback function will only receive the key of each element in the array

If the callback parameter is set to null, the default behavior is to remove any elements where the key is considered "falsey"

That is why when you use array_filter with null as the callback and the "ARRAY_FILTER_USE_BOTH" flag, the function will only remove elements where the value is empty, not where the key is empty.

So, to filter out all elements where either the key or value is empty and return and array containing only the non-empty elements, try this:

function filter_empty($key, $value) { return !(empty($key) || empty($value)); } $array = [''=>'2',0=>'3',0,5=>3,null,'',[]]; $result = array_filter($array, 'filter_empty', ARRAY_FILTER_USE_BOTH);