Conclusion

• Interfaces allow us to implement the same function with different behavior for different types.
• Functions taking one or more interface implementations as arguments are called constrained functions.
• Interfaces can be organized hierarchically by extending other interfaces.
• Interfaces implementations can themselves be constrained requiring other implementations to be available.
• Interface functions can be given a default implementation, which can be overridden by implementers, for instance for reasons of efficiency.
• Certain interfaces allow us to use literal values such as string or integer literals for our own data types.

Note, that I did not yet tell the whole story about literal values in this section. More details for using literals with types that accept only a restricted set of values can be found in the chapter about primitives.

What's next

In the next chapter, we have a closer look at functions and their types. We will learn about named arguments, implicit arguments, and erased arguments as well as some constructors for implementing more complex functions.