If you’re doing anything financial in Brazil, you have to manage “CNPJ” numbers. These numbers are unique identifiers for every business and every branch of that business, along with a pair of check-digits to validate that it’s a correct code. Everyone from banks to accountants to businesses needs to track and manage these.

When Patria joined a microscopic startup as an intern. The startup made an accounting package, and thus needed to track CNPJs. She asked the lead developer, “Hey, how do I validate those check-digits?”

Oma was tracking down a bug where the application complained about the wrong parameters being passed to an API. As she traced through the Java code, she spotted a construct like this:

Long s = foo.getStatusCode();
if (s != null) {
    //do stuff
} else {
    //raise an error
}

Learning about data structures- when to use them, how to use them, and why- is a make-or-break moment for a lot of programmers. Some programmers master this. Some just get as far as hash maps and call it a day, and some… get inventive.

Let’s say, for example, that you’re Jim J’s coworker. You have an object called a Closing. A Closing links two Entrys. This link is directed, so entry 1->2 is one Closing, while 2->1 is another. In real-world practice, though, two Closings that are linked together in both directions should generally be interacted with as pairs. So, 1->2 and 2->1 may not be the same object, but they’re clearly related.

UUIDs and GUIDs aren’t as hard as dates, but boy, do they get hard, don’t they. Just look at how many times they come up. It’s hard to generate a value that’s guaranteed to be unique. And there’s a lot of ways to do it- depending on your needs, there are some UUIDs that can be sorted sequentially, some which can be fully random, some which rely on hash algorithms, and so on.

Of course, that means, for example, your UUIDs aren’t sequential. Even with time-based, they’re not in sequence. They’re just sortable.

Bogdan Olteanu picked up a simple-sounding bug. There was a drop-down list in the application which was missing a few entries. Since this section of the app wasn't data-driven, that meant someone messed up when hard-coding the entries into the dropdown.

Bogdan was correct. Someone messed up, alright.