[ruby-core:101035] [Ruby master Feature#17339] Semantic grouping with BigDecimal#to_s

Issue #17339 has been updated by chumaltd (Takahiro Chuma).


I read doc again, and understand the situation.

If we have a chance to change API, another formatting option like `#to_s('G')` can be good that works as '3F'.
Then we'll have beautiful 'E', 'F', 'G' options.

As I referred, SI confirmed 3 digit grouping  policy twice(1948 and 2003). Other than 3 is not preferred way.
I think financial or business common practices follow 3 digit rule, too.

So, grouping option should have its default, and formatting with digit like '5F' will be more private.

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Feature #17339: Semantic grouping with BigDecimal#to_s
https://bugs.ruby-lang.org/issues/17339#change-88706

* Author: chumaltd (Takahiro Chuma)
* Status: Open
* Priority: Normal
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# Abstract
Thousands, millions, ... should be expressible with `BigDecimal#to_s`.

# Background
`BigDecimal('1234567').to_s('3F')` returns "123 456 7.0".

# Proposal
  - Have an option with which `BigDecimal('1234567').to_s('3F')` returns "_1 234 567_.0".
  - With decimal, `BigDecimal('1234567.8901234').to_s('3F')` should return "1 234 567.890 123 4".
  - Default behavior should be the above in long term.
  - And/Or, it would be nice to have a pretty method name. I think #to_s('3F') has universal use cases like money calculation.

# Discussion
  - International System of Units aka SI defines 3-digit-grouping on long numeric sequence.
    https://www1.bipm.org/jsp/en/ViewCGPMResolution.jsp?CGPM=22&RES=10
  - Original discussion in 1948 shows some example of 3-digit-grouping.
    https://www1.bipm.org/utils/common/pdf/CGPM/CGPM9.pdf#page=117

# Summary
  We want to have a natural format.



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