Nigel Tao

Using Go Without Generics

Go 1.17 was recently released, per the “release twice a year” schedule. As always, there’s a bunch of commentators noting that it still doesn’t have generics yet (it’s a work in progress and there’s a lot of work). Sometimes this is expressed as if Go code must therefore be littered with numerous uses of the empty interface{} type.

Here’s one counter-anecdote, where interface{} just isn’t that frequent, whether that’s “interface{} approximating generics” or otherwise. The Wuffs codebase is about 60k lines of Go code. Even after accounting that about 25% of that is a generated data table (the Wuffs compiler’s pre-parsed equivalent of arm_neon.h), it’s still not a small or toy set of programs:

$ git show | head -n 1
commit 1d191576683c97e8e3c59258f7dca9a010a10754
$ find . -name *.go | xargs wc -l | tail -n 1
60106 total
$ wc -l lib/armneonintrinsics/data.go
16713 lib/armneonintrinsics/data.go

In that whole corpus, interface{} is only used three times.

$ rg 'interface\{\}'
69:func debugf(format string, a ...interface{}) {

100:type dir map[string]interface{}

232:func (b *buffer) printf(format string, args ...interface{}) { fmt.Fprintf(b, format, args...) }

Two of those three simply mimic the fmt.Printf signature, whose arguments can indeed have varied types.

The last one, in a 99 line program, admittedly does use interface{} where other languages would use some sort of type-safe enum or union. But I don’t think generics would change anything here.

In a similar vein, this repository full of Go code also doesn’t use reflection at all, other than a couple of reflect.DeepEqual calls in tests:

$ find . -name *.go | xargs rg -w reflect
21:     "reflect"
167:    if !reflect.DeepEqual(got, want) {

18:     "reflect"
35:     if !reflect.DeepEqual(got, want) {

In conclusion, yes, generics are useful, and plenty of people want them in Go, for good reason. But you can also still get plenty done in Go without them.

Published: 2021-08-22