I started using Go back around 2015 and was immediately surprised by the lack of a generic type system. Sure, the empty interface{} existed, but that was hardly the same. At first I thought I wanted needed generics in Go, but over time I began appreciating the simplicity of the language. Therefore I was ambivalent at best when I learned of discussions to introduce generics in Go 2.0, and once the timetable was accelerated to 1.18, I decided it was time to dig into the proposal.

After a while, I gained an appreciation for how generics are implemented with the same elegance as Golang itself, and this moved me to share my experience. Go generics the hard way is a culmination of the time I spent playing with this new feature and provides a hands-on approach to learning all about generics in Go.

• Labs: a hands-on approach to learning Go generics
• FAQ: answers to some of the most frequently asked questions regarding Go generics
• Links: links to related reference material and projects that use generics

1. Prerequisites: how to install the prerequisites required to run the examples in this repository
2. Hello world: a simple example using generics
3. Getting started: an introduction to go generics
4. Getting going: basic concepts explored
5. Internals: how generics are implemented in golang
6. Benchmarks: basic benchmarks for common patterns using generics
7. Lessons learned: lessons learned from digging into generics

• How are you using generics in the Go playground?
• What is T?
• What is this any I keep seeing everywhere?
• What does the tilde ~ do?
• Do Go generics use type erasure?

We can use the Go playground in “Go dev branch” mode to edit and run your program with generics.

The symbol T is often used when discussing generic types because T is the first letter of the word type. That is really all there is too it. Just like x or i are often the go-to variable names for loops, T is the go-to symbol for generic types.

For what is worth, K is often used when there is more than one generic type, ex. T, K.

The word any is a new, predeclared identifier and is equivalent to the empty interface in all ways. Simply put, writing and reading any is just more user friendly than interface{} 😃.

The ~ symbol is used to express that T may be satisfied by a defined or named type directly or by a type definition that has the same, underlying type as another defined or named type. To learn more about type constraints and the ~ symbol, please refer to the section Tilde ~.

Generics in Go are not implemented with type erasure. Please jump to Internals for more information.

• Type parameter proposal: the accepted proposal for introdicing generics to go
• Getting started with generics: a tutorial from the authors of go for getting started with generics
• Go language specification: the reference manual for the go language
• Go FAQ: frequently asked questions for go

• Controller-runtime: a write-up and patchset for implementing conditions logic, patch helpers, and simple reconcilers using generics
• Go collections: generic utility functions for dealing with collections in go
• go-generics-example: examples using generics