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Date: Wed, 18 Feb 2015 18:44:46 -0800
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To: Christoph Becker <cmbecker69@gmx.de>, 
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Subject: Re: [PHP-DEV] Digit separators for numeric literals
From: rasmus@lerdorf.com (Rasmus Lerdorf)

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On 02/18/2015 06:07 PM, Christoph Becker wrote:
> Hi internals!
>=20
> A while ago a question was asked on the php-general mailing list with
> regard to digit seperators in numeric literals[1].
>=20
> IMHO it might be a useful enhancement to allow such digit separators fo=
r
> numeric (integer and float) literals in PHP for better readability;
> several other languages already support them (such as Java, Perl, Ruby,=

> C#, Eiffel and C++14).
>=20
> Before attempting to draft a respective RFC, I'd like to get some
> feedback, whether this is generally considered to be useful, which
> character would be preferred (most other languages seem to allow the
> underscore, but an apostroph or maybe some other character might be
> reasonable as well), and which restrictions should be applied (e.g.
> arbitrary use of the separator, group thousands only, etc.)
>=20
> I'm looking forward to hear your opinion.  Thanks in advance.
>=20
> [1] <http://marc.info/?l=3Dphp-general&m=3D142143581810951&w=3D2>

I think it will be difficult to find a separator character that doesn't
make a mess of the grammar.

  my_func(1,999,999) obviously doesn't work
  my_func(1'999'999) as per C++14 clashes with our single-quoted strings
  my_func(1_999_999) like in ADA might work

but _999_ would need to work as well and _ is a valid char in a constant
so you can have a constant named _999_.

  - nope
  # nope
  @ nope
  ~ nope
  ! nope
  % nope
  ^ nope

We went through this for the namespace char, and there simply isn't a
typable single character left to use for something like this. _ is the
closest but it would require some changes and BC breaks which I am not
sure is worth for what appears to me to be a not-so critical feature.

Now if we went into Unicode territory, we could do it. eg.

  my_func(1=E1=9A=80999=E1=9A=80999) U+1680 (although it looks too much l=
ike a -)
  my_func(1=E2=81=9F999=E2=81=9F999) U+205F (mathematical space)
  my_func(1=D9=AC999=D9=AC999) U+066C (Arabic thousands separator)
  my_func(1=C2=B7999=C2=B7999) U+00B7 (middle dot)

The last one looks best to me, but we'd need a team of people working in
shifts to answer the, "How do I type this?" question.

-Rasmus



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