Except it’s not JSON specific. The article literally talks about how their function design was chosen for similarity with the v1 API. And I’d wager that the go team are planning on reusing that function signature for other encoders too. Or at least expecting it to be reused by the wider ecosystem.

If you want type safety then pass a struct to the marshal. Which is actually the idiomatic way to do it anyway. The type safety would be in that.

I’m not going to disagree with you that Gos type system is a rather blunt tool nor that Gos expressiveness is extremely rigid compared to many other popular languages. All of that is completely true. But I don’t agree that the v2 JSON API is a good example of that problem.