Bug #12980: Time - Time to return a Rational

• Status: Closed
• Assignee: akr (Akira Tanaka)
• Target version: -
• ruby -v: ruby 2.4.0dev (2016-11-25 trunk 56897) [x86_64-darwin15]
• Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN

[matsuda (Akira Matsuda)]

Currently subtracting a Time from a Time returns a Float, which I guess causes #12952

Is there any reason this doesn't return a Rational?

[matsuda (Akira Matsuda)]

Well, my assumption seems wrong.

0.5r.round also becomes 0, so this isn't really related to #12952
Still I'm wondering why Time - Time isn't Rational though.

[duerst (Martin Dürst)]

• Subject changed from Time - Time to return a Retional to Time - Time to return a Rational

[akr (Akira Tanaka)]

It is because ruby-dev:38446 by mame-san.

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/38446

[akr (Akira Tanaka)]

• Status changed from Open to Feedback

[mame (Yusuke Endoh)]

I think of one philosophical reason and one practical reason.

A philosophical reason: many Time objects are inherently inexact. Since a Rational is considered exact, returning a Rational might convey the wrong message that the Time objects are exact.

A practical reason: Time is often used for a simple benchmark tool. Consider "t = Time.now; ...; p Time.now - t" prints, such as (631882841/200000000) or (1590642983/500000000). It is difficult for human to read and compare the result.

[matsuda (Akira Matsuda)]

• Status changed from Feedback to Closed

All right. Sounds rational. Thank you for the explanation, Mame-san and akr-san!