[pcwalton]

Couldn't you do:

    func closeIfNecessary(object interface{}) {
        closable, needsClosing := object.(closable)
        if needsClosing {
            closable.close()
        }
    }

And then just do:

    func f(i interface{}) {
        defer closeIfNecessary(i)
        ...
    }

Doing it this way also saves you boilerplate by factoring the downcast out into a separate function.

[Groxx]

As long as you can always call .close() regardless of the code below, yep - that'd work, and is definitely more readable.

If you can't call it unless [some other conditions], it goes back to the same kind of problem though. "closable" may not be a good choice on my part, as they're often called unconditionally.