即使所有字段实际上都没有，php也显示'Empty'

Question

In this form I created, it checks if the fields are set and are empty. I made a class with two methods, areSet() as isset(), and areEmpty() as empty(). In the areEmpty() method, it is supposed to display "Empty" if all the fields are empty, but even when all the fields are filled up, it still displays "Empty". Is it because of the implode() function that I used? I need someone's help to point out the wrong with my code.

HTML

<form action="validate.php" method="post">
    <input type="text" name="firstname" placeholder="First Name" autocomplete="off"><br>
    <input type="text" name="lastname" placeholder="Last Name" autocomplete="off"><br>
    <input type="text" name="email" placeholder="Email" autocomplete="off"><br>
    <input type="text" name="username" placeholder="Username" autocomplete="off"><br>
    <input type="password" name="password" placeholder="Password" autocomplete="off"><br>
    <input type="password" name="passwordAgain" placeholder="Confirm password" autocomplete="off"><br>
    <input type="submit" value="Submit">
</form>

validate.php

<?php

require 'include/class.php';

if(Input::areSet('firstname','lastname','email','username','password','passwordAgain')) {
    if(Input::areEmpty('firstname','lastname','email','username','password','passwordAgain')) {
        echo 'Empty';
    } else {
        echo 'Not empty';
    }
}

class.php

<?php

class Input {
    // isset()
    public static function areSet(...$fields) {
        $setFieldsArray = [];

        foreach($fields as $field) {
            $setFieldsArray[] = $_POST[$field];
        }

        return isset($setFieldsArray);
    }

    // empty()
    public static function areEmpty(...$fields) {
        $emptyFieldsArray = [];

        foreach($fields as $field) {
            $emptyFieldsArray[] = empty($_POST[$field]);
        }

        return implode(' || ', $emptyFieldsArray);
    }
}

Answer 1

I have no idea what you're doing there by setting an array and then returning an imploded array; but just loop through the $fields, check if the associated $_POST variable is empty and return true if so and at the end false if none are empty:

public static function areEmpty(...$fields) {

    foreach($fields as $field) {
        if(empty($_POST[$field])) {
            return true; // something was empty
        }
    }
    return false; // none were empty
}

You'll have issues with areSet() as well, because you loop $fields and set an array element of $setFieldsArray and then return if it is empty, which it will never be empty because you create array elements in it.