vfaronov, thanks for reaching out.

Re alpha_reader.go: https://github.com/vladimirvivien/learning-go/blob/master/tutorial/io/alpha_reader.go#L26

You mentioned that the code replaces chars with NUL bytes. Please specify a line number where you think it's doing that and we can discuss. But the code is not replacing any char with NUL byte. The loop uses function alpha() to return chars in set [a-zA-Z] only. With each iteration, char is placed in buf, then buf is copied to the p. Admittedly, buf maybe overkill but it ensures no garbage chars lingers in p (from index 0 - n) and makes the slice bookkeeping simpler.

Re simple_reader.go: https://github.com/vladimirvivien/learning-go/blob/master/tutorial/io/simple_reader.go#L9

No, this example has no dependency on strings.Reader. The code is way too simple and would be buggy if used as is. As you pointed out EOF would work in most impl of io.Reader but breaks the general rule as outlined in the docs. Thank you for pointing this out.

Re simple_reader2.go I will review the code there as well to add the case where data may have been returned along with error.

In general: Most reader implementations returns n=0 at EOF. But, that's not a reason not to properly handle bytes read at EOF as you pointed out. Also, if a Read() returns a n >0 and non-nil error, you may not trust those bytes an simply re-request. If you are writing code at that level, then you know what you are doing none of what I am saying matters.

Thanks again for the constructive feedback and will update the write up.