Sorry to double post, I missed the cross-post. On Fri, Dec 4, 2015 at 7:42 PM, EuanM <euanmee@gmail.com> wrote:
I'm currently groping my way to seeing how feature-complete our Unicode support is. I am doing this to establish what still needs to be done to provide full Unicode support.
This seems to me to be an area where it would be best to write it once, and then have the same codebase incorporated into the Smalltalks that most share a common ancestry.
I am keen to get: equality-testing for strings; sortability for strings which have ligatures and diacritic characters; and correct round-tripping of data.
Call to action: ==========
If you have comments on these proposals - such as "but we already have that facility" or "the reason we do not have these facilities is because they are dog-slow" - please let me know them.
If you would like to help out, please let me know.
If you have Unicode experience and expertise, and would like to be, or would be willing to be, in the 'council of experts' for this project, please let me know.
If you have comments or ideas on anything mentioned in this email
In the first instance, the initiative's website will be: http://smalltalk.uk.to/unicode.html
I have created a SqueakSource.com project called UnicodeSupport
I want to avoid re-inventing any facilities which already exist. Except where they prevent us reaching the goals of: - sortable UTF8 strings - sortable UTF16 strings - equivalence testing of 2 UTF8 strings - equivalence testing of 2 UTF16 strings - round-tripping UTF8 strings through Smalltalk - roundtripping UTF16 strings through Smalltalk. As I understand it, we have limited Unicode support atm.
Current state of play =============== ByteString gets converted to WideString when need is automagically detected.
Is there anything else that currently exists?
Definition of Terms ============== A quick definition of terms before I go any further:
Standard terms from the Unicode standard =============================== a compatibility character : an additional encoding of a *normal* character, for compatibility and round-trip conversion purposes. For instance, a 1-byte encoding of a Latin character with a diacritic.
Made-up terms ============ a convenience codepoint : a single codepoint which represents an item that is also encoded as a string of codepoints.
(I tend to use the terms compatibility character and compatibility codepoint interchangably. The standard only refers to them as compatibility characters. However, the standard is determined to emphasise that characters are abstract and that codepoints are concrete. So I think it is often more useful and productive to think of compatibility or convenience codepoints).
a composed character : a character made up of several codepoints
Unicode encoding explained ===================== A convenience codepoint can therefore be thought of as a code point used for a character which also has a composed form.
The way Unicode works is that sometimes you can encode a character in one byte, sometimes not. Sometimes you can encode it in two bytes, sometimes not.
You can therefore have a long stream of ASCII which is single-byte Unicode. If there is an occasional Cyrillic or Greek character in the stream, it would be represented either by a compatibility character or by a multi-byte combination.
Using compatibility characters can prevent proper sorting and equivalence testing.
Using "pure" Unicode, ie. "normal encodings", can cause compatibility and round-tripping probelms. Although avoiding them can *also* cause compatibility issues and round-tripping problems.
Currently my thinking is:
a Utf8String class an Ordered collection, with 1 byte characters as the modal element, but short arrays of wider strings where necessary a Utf16String class an Ordered collection, with 2 byte characters as the modal element, but short arrays of wider strings beginning with a 2-byte endianness indicator.
Utf8Strings sometimes need to be sortable, and sometimes need to be compatible.
So my thinking is that Utf8String will contain convenience codepoints, for round-tripping. And where there are multiple convenience codepoints for a character, that it standardises on one.
And that there is a Utf8SortableString which uses *only* normal characters.
We then need methods to convert between the two.
aUtf8String asUtf8SortableString
and
aUtf8SortableString asUtf8String
Sort orders are culture and context dependent - Sweden and Germany have different sort orders for the same diacritic-ed characters. Some countries have one order in general usage, and another for specific usages, such as phone directories (e.g. UK and France)
Similarly for Utf16 : Utf16String and Utf16SortableString and conversion methods
A list of sorted words would be a SortedCollection, and there could be pre-prepared sortBlocks for them, e.g. frPhoneBookOrder, deOrder, seOrder, ukOrder, etc
along the lines of aListOfWords := SortedCollection sortBlock: deOrder
If a word is either a Utf8SortableString, or a well-formed Utf8String, then we can perform equivalence testing on them trivially.
To make sure a Utf8String is well formed, we would need to have a way of cleaning up any convenience codepoints which were valid, but which were for a character which has multiple equally-valid alternative convenience codepoints, and for which the string currently had the "wrong" convenience codepoint. (i.e for any character with valid alternative convenience codepoints, we would choose one to be in the well-formed Utf8String, and we would need a method for cleaning the alternative convenience codepoints out of the string, and replacing them with the chosen approved convenience codepoint.
aUtf8String cleanUtf8String
With WideString, a lot of the issues disappear - except round-tripping(although I'm sure I have seen something recently about 4-byte strings that also have an additional bit. Which would make some Unicode characters 5-bytes long.)
(I'm starting to zone out now - if I've overlooked anything - obvious, subtle, or somewhere in between, please let me know)
Cheers, Euan
Good initiative. Here is some info I've bookmarked over time... http://www.joelonsoftware.com/articles/Unicode.html
The Single Most Important Fact About Encodings - It does not make sense to have a string without knowing what encoding it uses. You can no longer stick your head in the sand and pretend that "plain" text is ASCII. There Ain't No Such Thing As Plain Text. If you have a string, in memory, in a file, or in an email message, you have to know what encoding it is in or you cannot interpret it or display it to users correctly.
http://kunststube.net/encoding/
So what does it mean for a language to natively support or not support Unicode? It basically refers to whether the language assumes that one character equals one byte or not. What does it mean for a language to support Unicode then? Javascript for example supports Unicode. In fact, any string in Javascript is UTF-16 encoded. In fact, it's the only thing Javascript deals with. You cannot have a string in Javascript that is not UTF-16 encoded. Javascript worships Unicode to the extent that there's no facility to deal with any other encoding in the core language. Other languages are simply encoding-aware. Internally they store strings in a particular encoding,
http://cafe.elharo.com/programming/the-ten-commandments-of-unicode/
1. I am Unicode, thy character set. Thou shalt have no other character sets before me. 4. Thou shalt not refer to Unicode as a two-byte character set. 6. Thou shalt count and index Unicode characters, not UTF-16 code points. 7. Thou shalt use UTF-8 as the preferred encoding wherever possible.
ruomuh
https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conce...
Strings and Characters in Swift
http://oleb.net/blog/2014/07/swift-strings/ Interesting article, though I don't yet grok it all, I thought it worth sharing...
Swiftʼs string implemenation makes working with Unicode easier and significantly less error-prone. Strings in Swift are represented by the String type. A String is a collection of Charactervalues. A Swift Character represents one perceived character (what a person thinks of as a single character, called a grapheme). Since Unicode often uses two or more code points(called a grapheme cluster) to form one perceived character, this implies that a Charactercan be composed of multiple Unicode scalar values if they form a single grapheme cluster. (Unicode scalar is the term for any Unicode code point except surrogate pair characters, which are used to encode UTF-16.) This change has the potential to prevent many common errors when dealing with string lengths or substrings. It is a huge difference to most other Unicode-aware string libraries (including NSString) where the building blocks of a string are usually UTF-16 code units or single Unicode scalars.
cheers -ben