[ruby-core:48447] [ruby-trunk - Feature #6973][Assigned] Add an #integral? method to Numeric to test for whole-number values

Issue #6973 has been updated by mame (Yusuke Endoh).

Status changed from Open to Assigned
Assignee changed from mame (Yusuke Endoh) to mrkn (Kenta Murata)
Target version changed from 2.0.0 to next minor

I think mrkn is eligible to handle this ticket.
The following is my personal comment.

regularfry (Alex Young) wrote:
>  > Personally, I'm not entirely convinced this method is a good idea.
>  > With Floats, you can't really guarantee that "4.0" is the same as
>  > "4". It could actually be "4.00000000000000001" but the precision is
>  > lost.
>  
>  This is actually not true.  If you have a float with a value of 4.0, 
>  then that genuinely *is* the same as 4.  The whole number value "4" has 
>  a precise representation in floating point format, and if you have that 
>  value then it makes no sense to say that what you have might not be 
>  equal to 4.
>
>  Floats are precise, just like Integers are.  *Operations* on floats are 
>  not accurate, and that's where the confusion comes from.  That's 
>  inherent to the representation and something you've got to deal with 
>  anyway, so I certainly don't see this test as making that problem worse.

Your points is valid as long as we can distinguish a Float that includes
error from a Float that includes no error, such as, just created by a
Float literal, or by only accurate operations (no overflow, no indivisible
division, ...).
But in fact, we cannot distinguish them.  We conservatively have to think
that any Float object includes an error, I think.

-- 
Yusuke Endoh <[e-mail]>
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Feature #6973: Add an #integral? method to Numeric to test for whole-number values
https://bugs.ruby-lang.org/issues/6973#change-31775

Author: regularfry (Alex Young)
Status: Assigned
Priority: Normal
Assignee: mrkn (Kenta Murata)
Category: core
Target version: next minor


Numeric#integer? checks whether an instance is an Integer.  It is often useful to check whether the value of a non-Integer variable is actually a whole number, and the #integer? method doesn't help here.

This patch adds Numeric#integral?, which performs this check.


-- 
http://bugs.ruby-lang.org/