[Sphax]

I was looking for the example proxy around http.ResponseWriter the author talked about which is implemented in Goji, I believe it's this code: https://github.com/zenazn/goji/blob/master/graceful/middlewa...

I understand it fine except this bit right at the end:

    var _ http.CloseNotifier = &fancyWriter{}
    var _ http.Flusher = &fancyWriter{}
    var _ http.Hijacker = &fancyWriter{}
    var _ io.ReaderFrom = &fancyWriter{}

What's the purpose of this ? According to effective go this just silences the unused imports but I don't think there's a need for that here.

[rakoo]

The relevant part of Effective Go is here: http://golang.org/doc/effective_go.html#blank_implements

It allows you to make sure fancyWriter implements all those interfaces, so that any future refactoring that breaks compatibility breaks at compile time.

You know how Go makes interfaces concordance implicit ? Whatever has a Read() method is a io.Reader without asking for it ? This explicitly tells the compiler (and other developers) the same thing.

[Sphax]

Thank you, I read the wrong part of effective Go apparently, didn't see this. It's clear now.

[iand]

They are static assertions that fancyWriter implements all those interfaces. They are compiled away to nothing but provide a kind of test of correctness.

[Sphax]

Oh, ok, makes sense. Thank you.