[ruby-core:99191] [Ruby master Feature#16470] Issue with nanoseconds in Time#inspect

Issue #16470 has been updated by mame (Yusuke Endoh).


We need to understand the use case precisely.  Does OP want to pass a general Float value to `Time.utc`?  Or does he just want to specify nanosecond?

I think of no practical use case for the former (passing a general/calculated Float).  If we need to specify nanosecond, I don't think that Float is a good API for that.  `Time.utc(2007, 11, 1, 15, 25, 0, nanosecond: 123456789)` or something is better.


In addition, the following point is wrong.

> The nanosecond value 8483885939586761/68719476736000000 can be expanded to 0.12345678900000001.

A correct expansion is `0.123456789000000004307366907596588134765625`.  So, which is better?

```
t.inspect # => "2007-11-01 15:25:00 8483885939586761/68719476736000000 UTC"
t.inspect # => "2007-11-01 15:25:00.123456789000000004307366907596588134765625 UTC"
```

Personally, I prefer the latter to the former because decimal is much easier to understand.

However, I'm afraid if the expansion might be very long. Truncation is a possible, of course. But, it will break the original reason why the fraction part is added in Time#inspect (#15958):

> But recently we encounters some troubles the comparison of Time objects whose frac parts are different.

So, naive truncation may bring the same troubles again. I guess nanosecond (nine digits after the decimal point) would be enough in many use cases, but I'm not 100% sure.

----------------------------------------
Feature #16470: Issue with nanoseconds in Time#inspect
https://bugs.ruby-lang.org/issues/16470#change-86572

* Author: andrykonchin (Andrew Konchin)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
Ruby 2.7 added nanosecond representation to the return value of `Time#inspect` method.

Nanosecond is displayed as `Rational` as in the following example:

```ruby
t = Time.utc(2007, 11, 1, 15, 25, 0, 123456.789)
t.inspect # => "2007-11-01 15:25:00 8483885939586761/68719476736000000 UTC"
```

The nanosecond value `8483885939586761/68719476736000000` can be expanded to `0.12345678900000001`. This is different from the stored nanosecond:

```ruby
t.nsec # => 123456789
t.strftime("%N") # => "123456789"
```

I assume it isn't expected, and will be fixed.



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