[abound]

There are at least two places in the standard library that behave like this: sql.ErrNoRows and the error thrown by os.Open when a file doesn't exist.

[manlobster]

True, but both of these are for relatively slow operations, where the performance of the error checking is relatively insignificant.

[zachmu]

It has also become somewhat common to use io.EOF to signal the end of iteration, like the reader libraries do.