We often work with types that are far too general or hold far too many values than what is necessary in our domains. In our past episode on algebraic data types we used algebra to help simplify certain types to chisel them down to their core essentials. However, sometimes that isn’t possible. Sometimes we just want to differentiate between two seemingly equivalent values at the type level.

For example, an email address is nothing but a string, but it should be restricted in the ways in which it can be used. Also, ids in our code may all be integers, but it doesn’t make sense to compare a user’s id with, say, a subscription id. They are completely different entities.

We want to show that Swift, and in particular Swift 4.1, gives us an incredible tool to lift types up to a higher level so that they can distinguished from each other more easily. This helps improve the contracts we are building into our functions and methods, and overall makes our code safer.