The Japanese issue appears to be saying that there's a problem in RubySpec that will need to be fixed, and that fixing it is a problem with (I think?) early 1.9 compatibility.

Float#round returns Fixnum value when the argument is 0 or omitted.

irb(main):005:0> 12.34.round.class
=> Fixnum
irb(main):006:0> 12.34.round(0).class
=> Fixnum

If we will fix BigDecimal#round, we should change the return value for the case of the argument 0 is supplied.

Good point, I didn't catch that. If it was up to me I'd rather have Float#round always return Float as well for consistency. I could work on a for that too if you agree.

We need matz's approval to change Float#round.

We (mainly mrkn and matz) discussed why Fixnum#round returns Integer today. The answer is because (unlike other languages, namely C's round(3)) in ruby we can safely store all possible return value that round can theoretically generate, in Integer.

BigDecimal#round's returning BigDecimal instance sounds nice. But matz said he need to think a while for this historic Float behaviour.

#round with the argument less than 1 (n < 1) should return Integer value.

Matz.