[jamespwilliams]

That err == nil check was added very recently and isn’t included in the latest Go release, which the author used in this article.

[esprehn]

Ah ha! So the issue was always going through the error type reflection even for the success path.

https://github.com/golang/go/commit/af43932c20d5b59cdffca454...

I'd be interesting to see the benchmark after that.