Dont understand this

[phpmaster57]

So I am looking at the code for https://github.com/vlucas/valitron/blob/master/src/Valitron/Validator.php a validation library, and currently trying to interpret the code. Most of it I understand but a part in the constructor is confusing me. It is as follows:

public function __construct($data, $fields = array(), $lang = null, $langDir = null)
    {
        // Allows filtering of used input fields against optional second array of field names allowed
        // This is useful for limiting raw $_POST or $_GET data to only known fields
        $this->_fields = !empty($fields) ? array_intersect_key($data, array_flip($fields)) : $data; 

The part that is confusing me is the $this->_fields line, what exactly is the point of this and could you provide an example for when this when be needed? The part that really gets me is when it gets to array_intersect_key and array_flip, again what is the point of these?

 

[QuickOldCar]

ternary operator

 

Same as an if/else, shortened

[Jacques1]

The array_intersect_key() stuff is a very obscure way of removing all ($key, $value) pairs from $data where $key isn't in $fields.

 

So $fields is basically a whitelist of allowed keys (as explained in the comments).

[QuickOldCar]

Not sure what I was thinking, maybe another coffee in order.

[phpmaster57]

So what is the point of array_flip() on $fields, when you can pass in  a normal array such as: ['username','pass','email'] to $fields.

[Jacques1]

The point is to turn the array values of $fields into keys so that they can be passed to array_intersect_key():

<?php

$fields = ['username', 'pass', 'email'];
var_dump($fields);

$flipped_fields = array_flip($fields);
var_dump($flipped_fields);

Using $fields directly wouldn't work, because it has numerical keys which aren't very useful here.

Edited February 15, 2016 by Jacques1