Go Get Interfaced: Enums in Golang

Golang, Interfaces, and Enums

So here’s a nice golang idiom that I ran across years ago that I found generally useful. Golang, unlike languages like c doesn’t natively support enumerations. Instead, constants typically are used when creating a list of enumerations. But, go is a strongly-typed language, so we can do better than simply using constants - we can type our enumeration with the use of a type declaration.

type DogState uint

By defining a type for our enumeration, we can consistently pass and return typed-values among our functions operating on our enumeration. Okay, that’s all well and good, but what happens when we want to go between uint values and string representations of those values; a commonly used paradigm when working with enumerations. One approach would have us write mapping functions that might switch among the values to return a string. Or, when going from a string name of an enumeration to the uint value, we might use a map[string]. That’s a doable implementation, but there’s an easier, and more idiomatic way.

Gogo

Here we gogo!

Years ago, I wrote an interesting article that I thought might be worth re-posting (and revising) here on my blog. For a while I got into programming in golang and in the early going (pun-alert!), there were a lot of idioms that were not well understood by a noob. One of those paradigms was channels, go-routines, and signals used simultaneously. Taken separately, they are more easily understood. But when taken together, there can be some confusion. In this article, I address how to properly establish a signal-handler and a channel to terminate go-routines when the user interrupts the program with a signal such as ctrl-c or kill(1).

Recursion Revisited

Recursion, from more than one point-of-view.

A common programming idiom in computer science is solving a problem by self-reference, also known as recursion. In this post, we look at two different implementations of the same problem.

Solve a recursive problem in two different programming language paradigms

Let’s look at the solution to a simple problem, compute $f(x)=e^{x}$.

We will illustrate two separate solutions - one in a procedural language (python), and the other in a functional language (elixir).

Let’s start off with the functional language. Were does recursion come into play?

We define the function $f(x)=e^x$ as the infinite sum, $\text{ }f(x) = \sum_{n=0}^\infty{\frac{x^n}{n!}}$

In our solution below, we define two separate recursive functions, exp/2 and fac/1. What’s interesting to note here is how each of these functions has two separate definitions. This is an aspect of programming in elixir that elegantly uses pattern-matching to return different results depending upon the input. Our two functions nicely dovetail into the base-case and recursive case of a recursive algorithm.

For example, looking at exp/2, the first function definition returns 1 for any value of x (as indicated by the _ preceding the variable) and returns 1. This is the mathematical equivalent of $x^0=1\text{ for any }x$.

The second definition of exp/2 is the recursive case. for any value of $n\gt0$. Moreover, we define exp(x, n) as $\frac{e^x}{n!}$ + exp(x, n-1).

Similarly for the definition of fac/1 we see two definitions; one for $n=0$ and another for all values of $n\gt0$.