PHP - refactoring this if statement to avoid duplication - php

Question

In this snippet of code we type $inputs['user_id'] 3 times.
if (isset($inputs['user_id']) && $inputs['user_id']) { // The consumer is passing a user_id
doSomethingWith($inputs['user_id']);
}
What's the most readable and robust refactoring I can do to avoid the duplication and avoid any notice that the index user_id doesn't exist?
Thanks.

Answer 1

Here nothing is wrong with the duplication. You cannot assign $inputs['user_id'] to a variable before checking if it is set, otherwise this will produce a Notice undefined index ....
The only thing here could be done is to omit the isset call and use !empty instead, like this:
if(!empty($inputs['user_id'])) {
doSomething($inputs['user_id']);
}
Now You are only typing it twice and the check
!empty($inputs['user_id'])
equals to
isset($inputs['user_id']) && $inputs['user_id']
EDIT: based on a comments, here is a quote from documentation:
The following things are considered to be empty:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)
So either empty(0) or empty('0') will return true, that means
if(!empty('0') || !empty(0)) { echo "SCREW YOU!"; }
will echo nothing... Or, in polite way, I will repeat the statement above:
!empty($inputs['user_id']) === (isset($inputs['user_id']) && $inputs['user_id'])
EDIT 2:
By omitting the isset and replacing by !empty the variable is still checked, whether the index is already set, please read the documentation, which says:
No warning is generated if the variable does not exist. That means empty() is essentially the concise equivalent to !isset($var) || $var == false.

Answer 2

What about this:
// put validation check to the function body
function doSomethingWith($userId) {
if($userId === -1) {
// if this is not a valid user id -> return
return;
}
// do something ...
}
// initalize $user with proper default values.
// doing so you can be sure that the index exists
$user = array(
'id' => -1,
'name' => '',
...
);
// merge inputs with default values:
$user = array_merge($user, $request);
// now you can just pass the value:
doSomethingWith($user['id']);

Answer 3

Below might not be the best way for every situation, but definitely cuts down on the repetition.
Your example code would turn into:
doSomethingWith($inputs['user_id']);
and your function would look like this (notice the argument supplied by reference, to avoid the undefined variable warning):
function doSomethingWith(&$userID) {
if (empty($userID)) return;
// ... actual code here ...
}

Answer 4

Assuming that 0 and "" and null are not valid user_ids:
if ($id = $inputs['user_id']) {
doer($id);
}
YOu can also do with evil # to avoid notice in your logs, (I don't like this way):
if ($id = #$inputs['user_id']) {
doer($id);
}