rlibaert

#golang

2025

Advanced flag parsing in standard Go

Over time, a plethora of libraries were developed to build complex CLI applications; spf13/cobra and urfave/cli being probably the most used ones (both have tens of thousands stars on GitHub). While they offer lots of features out of the box, I often found them complex and overkill for my needs. In this post, we will have an overview of how Go’s flag works and see some advanced uses of it. We will then try to implement parsing of complex values such as comma-separated arguments or slices.

4 min read

Making sync package type strict using Go generics

The sync package from Go’s standard library provides primitives (Mutex, WaitGroup, …) to help solving synchronization problems. This is an older package and some of the implementations could be different if the generic features were available then. Indeed, the sync.Pool and sync.Map facilitates concurrent usage for storing and retrieving data in different situations. Those features are pretty elementary and their functionality highly relies on the fact that they can be used with any type, which comes with a few drawbacks. Giving up the type strictness prevents the compiler to detect potential errors or requires type assertion code. The former implies extra attention when writing code and the latter reduces its simplicity and readability.

4 min read

Must pattern in Go and a generics-based generalization

There is a handy code pattern commonly found in Go codebases, known as Must pattern. To put it simply, for a given Do function returning at least an error, the MustDo function then omits returning the error, panicking instead. For instance: // package regexp func Compile(expr string) (*Regexp, error) func MustCompile(expr string) *Regexp // package netip func ParseAddr(s string) (Addr, error) func MustParseAddr(s string) Addr In contexts where errors are unlikely to happen, it is a nice way to still handle them while uncluttering the code. Of course this implies the application of the same good practices as when using panic. Those functions are often used to create constant-like objects, such as regular expressions:

2 min read