Programming with Types

Chapter 4. Type safety

This chapter covers

• Avoiding the primitive obsession antipattern
• Enforcing constraints during instance construction
• Increasing safety by adding type information
• Increasing flexibility by hiding and restoring type information

Now that we know how to use the basic types provided by our programming language and how to compose them to create new types, let’s look at how we can make our programs safer by using types. By safer, I mean reducing the opportunity for bugs.

There are a couple of ways to achieve this by creating new types that encode additional information: meanings and guarantees. The former, which we’ll cover in the first section, removes the opportunity for us to misinterpret a value, such as mistaking a mile ...