[ruby-core:31960] Re: not use system for default encoding

> It strikes me as a bit "scary" to use system locale settings to *arbitrarily*
> set Encoding.default_external

What do you mean by “arbitrarily”? The algorithm used
(i.e. http://goo.gl/soW7) is pretty straightforward. Presumably
a user’s locale encoding reflects that in which he prefers to work.

> For example, I develop on windows (def: IBM437).  This means that if I want
> this to work cross platform I have to specify IBM437 for every File.read (et
> al) that I use in my library.  So it is a bit scary.

Well, firstly, that’s a pretty odd encoding to use. In general, you’ll have a
far easier time if you use UTF-8 for everything, and legacy encodings only when
necessary or, possibly, writing in a CJK script. In any case, even if you
continue using that encoding, the external encoding only needs to be specified
explicitly if the files contain non-ASCII characters. And if they do, and
interoperability is your goal, then why are you using IBM437 in the first
place?

> Suggestion: default to UTF-8 *no matter where* then allow the user to change
> it if they want something else.

That stands in opposition to the design goals of Ruby’s M17N. See Naruse’s
article at http://goo.gl/Xy20 for the background. Or, to put it another way,
Ruby’s system was designed by encoding experts, including Unicode Consortium
member Martin J. Dürst, and still explicitly rejects defaulting to UTF-8.

> Or even default to BINARY (ASCII-8BIT) unless they specify.  Most users don't
> want/need encoding until they run into it--they can handle it then.

That was the philosophy of English-centric software development for many years,
but global distribution and the web discredited it. Users don’t think they care
about encoding, but then they process input containing non-ASCII byte
sequences, and everything blows up. For example, consider the following “binary”
representations of e acute:

  Encoding.list.map{|n| "é".encode(n).dump rescue nil}.compact.uniq
  #=> [""\\u{e9}"", ""\\x88m"", ""\\xA0\\xC1"", ""\\x8F\\xAB\\xB1"",
  ""\\xA8\\xA6"", ""\\xE9"", ""\\x00\\xE9".force_encoding("UTF-16BE")",
  ""\\xE9\\x00".force_encoding("UTF-16LE")",
  ""\\x00\\x00\\x00\\xE9".force_encoding("UTF-32BE")",
  ""\\xE9\\x00\\x00\\x00".force_encoding("UTF-32LE")", ""\\x82"", ""\\x8E"",
  ""e\\xCC\\x81"", ""\\xC3\\xA9""]

If you store text as byte sequences without associated encodings, how will you
display it? How do you pattern match against it? You can’t because the strategy
is "\\110\\97\\105\\118\\130", as IBM437 users would say, or, if you speak
GB2312, "\\110\\97\\105\\118\\168\\166". Ultimately, the closest you can get to
ignoring encodings while at the same time remaining interoperable, is by
storing data in a Unicode-compatible encoding—UTF-8 being the obvious general
choice—then transcoding your input into UTF-8. Even this requires that either
the input is tagged with an encoding, or you’re willing to use imperfect
heuristic algorithms to detect it.