Problem file

Author: AydinHassan

exercises/a-safe-space-for-nulls/problem/problem.md

@@ -0,0 +1,77 @@
+Create a program that exports a `User` object instance to a CSV file using the null safe operator to access it's member properties.
+
+You will have a variable named `$user` available in your PHP script. We will put it there, each time your program runs  and it will be populated with random data each time it runs.
+
+Sometimes, a number of the properties may not exist and will be null. 
+
+With the null safe operator it is possible to access variables like so:
+
+```php
+$capitalPopulation = $country?->capital?->population;
+```
+
+If the `capital` property is null, the variable `$capitalPopulation` will also contain null. Previously, without the null safe operator this would be achieved like so:
+
+```php
+$capitalPopulation = null;
+if ($city->capital !== null) {
+    $capitalPopulation = $country->capital->population;
+}
+```
+
+The `User` class, for which the `$user` variable holds an instance of, has the following signature:
+
+```php
+class User
+{
+    public string $firstName;
+    public string $lastName;
+    public ?int $age = null;
+    public ?Address $address = null;
+}
+
+class Address
+{
+    public int $number;
+    public string $addressLine1;
+    public ?string $addressLine2 = null;
+}
+```
+
+Note also the `Address` class which the property `$user->address` may be an instance of, or it may be null.
+
+Export the `$user` data to a CSV with the following columns:
+
+`First Name`, `Last Name`, `Age`, `House num`, `Addr 1`, `Addr 2`
+
+ * The CSV should be comma delimited
+ * The columns should read exactly as above, any mistake will trigger a failure
+ * There should be one row for the column headers and one for the data
+ * Any properties which are null on the user should be printed as empty fields in the CSV
+ * The file should be named `users.csv` and exist next to your submission file (eg in the same directory)
+ 
+And finally, the most important part, all properties which may be `NULL` should be accessed using the null safe operator!
+
+### Advantages of the null safe operator
+
+* Much less code for simple operations where null is a valid value
+* If the operator is part of a chain anything to the right of the null will not be executed, the statements will be short-circuited.
+* Can be used on methods where null coalescing cannot `$user->getCreatedAt()->format() ?? null` where `getCreatedAt()` could return null or a `\DateTime` instance
+
+----------------------------------------------------------------------
+## HINTS
+
+Remember your program will be passed no arguments. There will be a `User` object populated for you under the variable `$user`.
+It is available at the beginning of your script.
+
+Documentation on the Null Safe Operator can be found by pointing your browser here:
+[https://www.php.net/manual/en/language.oop5.basic.php#language.oop5.basic.nullsafe]()
+
+----------------------------------------------------------------------
+## EXTRA
+
+We have not given any hints regarding writing to a CSV file, as we are not testing you on that. You can do it however you please.
+
+Therefore, it is up to you to figure out how to write a CSV if you don't already know :)
+
+Okay... just one hint: Check back over the exercise "Have the Last Say". You might find some pointers there!