A Review of Nim 2: The Good and Bad with Example Code

Summary

I've been using Nim for about 1-2 years now, and I believe the language is undervalued. It's not perfect, of course, but it's pleasant to write and read. My personal website uses Nim. After reading a recent article on Nim ("Why Nim") and the associated HN comments, it's clear that comments and some information about Nim are misleading and outdated. Since Nim 2, a tracing Garbage Collector is not the default nor the recommended memory management option. Instead, the default memory management model is ORC/ARC, which supports C++-esque RAII with destructors, moves, and copies. When you use ref types, your object instances are reference-counted, similar to a shared_ptr in C++, but it does not include atomic counters by default (use the switch --mm:atomicArc, which will likely be the default in Nim 3*). In fact, you could use Nim as a production-ready alternative to the upcoming Carbon language. Nim has fantastic interoperability with C++, supporting templates, constructors, destructors, overloaded operators, etc. However, it does not compile to readable C or C++ code, which is unlike Carbon's goals. In this article, I review the good and bad parts of Nim 2. I'll write a tiny key/value file format that can load a user-declared object to demonstrate how some of Nim's features compose in powerful ways. Hopefully, this code example will give a good feel for the language. If you prefer to start with code, feel free to jump to the example first. I'm not going to discuss subjective dismissals of the language, such as whitespace or case insensitivity, which IMO are not reasons to dismiss a language. * The Nim team is currently working on Nim 3 (called Nimony), a new iteration of the language. The largest design change is NIF, an intermediate human-readable format (similar to Lisp). NIF enables incremental compilation, a better macro system (simpler to implement), and better tooling. Here is a link to a document describing the design and associated blog post. A common question I...