fmt: use public io.RuneScanner interface for ScanState reader All io.Reader that are passed to newScanState in all the standard library tests that implement io.RuneReader also implement io.RuneScanner. Do not check on each call ScanState's UnreadRune that the used RuneReader also implements the UnreadRune method by using a private interface. Instead require the used Reader to implement the public RuneScanner interface. The extra implementation logic for UnreadRune is removed from ScanState. Instead the readRune wrapper is extended to implement UnreadRune for the RuneScanner interface. If the Reader passed to newScanstate does not implement RuneScanner the readRune wrapper is used to implement the missing functionality. Note that a RuneReader that does not implement RuneScanner will also be wrapped by runeRead which was not the case before. Performance with the readRune wrapper is better than without before. Add benchmark to compare performance with and without using the readRune wrapper. name old time/op new time/op delta ScanInts-2 704µs ± 0% 615µs ± 1% -12.73% (p=0.000 n=20+20) ScanRecursiveInt-2 82.6ms ± 0% 51.4ms ± 0% -37.71% (p=0.000 n=20+20) ScanRecursiveIntReaderWrapper-2 85.1ms ± 0% 52.4ms ± 0% -38.36% (p=0.000 n=20+20) Change-Id: I8c6e85db9b87a8171caab12f020b6e256b498e81 Reviewed-on: https://go-review.googlesource.com/19895 Run-TryBot: Rob Pike <r@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org>
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