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> Java treats text as all modern systems should: as a sequence of the open-ended Universal Character Set (UCS)

unfortunately, Java treats text as data encoded in UCS-2 which uses a maximum of two bytes to represent a character and all the Java string APIs assume the UCS-2 encoding.

The problem with UCS-2 is that it doesn't allow to encode characters outside of the Unicode BMP.

In order to solve this, Java actually uses UTF-16 encoding to encode characters outside of the BMP, but none of the APIs actually know about this and still assume UCS-2.

This leads to the API being wrong about character lengths and to regular expressions wrongly matching certain strings and sometimes destroying data when you apply them to replace substrings.

Case in point is this little test class here: https://gist.github.com/5745601abbfbf7068fcd

which prints 2 on the console. I've also given a talk about this at a swiss JS conference in 2012: http://pilif.me/unicode.pdf - JS has/had the same issues as Java in that regard.

The only well-known contemporary languages that get this (somewhat) right are Perl (since forever), Python 3, Ruby 1.9 and Swift, though ES6 is in process of getting up to speed too.

Python 3 and Swift have the issue of being totally tied to unicode, so if the politics and issues around Han Unification matter to you then those two are actually also not usable for you.

> The only well-known contemporary languages that get this (somewhat) right are Python 3, Ruby 1.9 and Swift, though ES6 is in process of getting up to speed too.

And Perl.

You are right of course (I knew this as you can see when you look at the PDF I linked - slide 50). I have edited my original post.

> unfortunately, Java treats text as data encoded in UCS-2 which uses a maximum of two bytes to represent a character and all the Java string APIs assume the UCS-2 encoding.

Not entirely true. There are codePoint*, indexOf(int ch), and various other methods on String which do work correctly in code points. Unfortunately old methods can't be changed without affecting compatibility.

> The only well-known contemporary languages that get this (somewhat) right are...

and Ceylon.

"that get this (somewhat) right [...] and Swift"

I don't know how Perl, Ruby and Python handle this, but with Unicode, I don't think we can get better than 'somewhat right'.

For example, Swift removes some invariants on string operations that many people take for granted, such as:

  - appending to a string of length n doesn't change its first n characters.

  - appending a string of length m to one of length n gives you a string of length (m+n)

  - strings that are equal to each other have the same byte representation (=> whenever you use a set of strings, you have to choose whether you want the ability to get the same bytes out or not)

I also am not sure whether s==t and u==v implies s+u==t+v.

The example you've provided is confusion/complexity related to what a "character" is.

If a language supports a string type and related functions that equate "character" with a grapheme they'll deliver your first two invariants.

With an appropriate approach to byte representations your third invariant can also be maintained.

If you look at Swift, it uses what Apple calls "extended grapheme cluster" as its "Character" type.

That means:

   "e" + "`" = "è"

All three strings have 1 Swift Character in them; the first is not a prefix of the last.

And yes, you can normalize byte representations, but then you have to give up round-tripping through strings.

I maintain convinced that there is no way to do Unicode strings without drawbacks.

I haven't tried Swift yet but my latest observations and guessing about your grave accent example are as follows.

Based on direct cut/paste and inspection, the grave accent (in the "`" string above and here in these parens too) is codepoint 96. This is a non-combining (standalone) grave accent that is meant to be its own grapheme. Appending it to another grapheme such as "e" should not combine. The result should be an "e" followed by a visually separate grave character. The string should contain two separate graphemes and have a length of 2.

I can't tell if the confusion/complexity in this case is due to some cut/paste/storage/browser bug, or Swift's handling of the special case (called "degenerate" in the Unicode standard) of an isolated combining character that hasn't yet been combined, or something else.

So I read some of the Swift docs to see if that revealed anything.

The Swift docs I read used the example of appending a combining grave accent (ie codepoint 768, which is NOT the same as the codepoint 96 stored in "`", but rather something more akin to "̀"), stored as a Character value, to an "e" string, stored as a String value. After appending a Character that is a combining character, the length of the new String is the same as the old one. And that's appropriate.

I presume that the Swiftian character count concept, which is applicable to Swift Strings, and which is returned by .count, is inapplicable to Swift's Character values.

Presumably, when a Swift Character value needs to be displayed, Swift generates a String that contains it and displays that. Further, perhaps, if the Character value is a combining character, Swift automatically prepends an appropriate base character (a space, value 32, or NBSP, or dotted circle, or some such) to ensure it becomes its own grapheme.

Part of the confusion may stem from the decision in Swift to use "..." quotemarks for literals of both types. It seems you have to explicitly tell Swift that a "..." literal is a Character, not a String, if you want a Character. At first blush I like the sound of that.

Alternatively, they've screwed something up.

Python 3 and Swift have the issue of being totally tied to unicode, so if the politics and issues around Han Unification matter to you then those two are actually also not usable for you.

Those issues do matter to me, yet Unicode-based languages like Python 3 and Swift are not only usable, they are best general approach (among actually existing technologies, not among all theoretically possible approaches). I've been building Asian (CJK) infosystems since the 1980s, and there are far fewer problems with Unicode-based approaches than with the encoding soup we had before.

> Either way, switching to ISO 8859-1 for this makes no sense.

ISO 8859-1 has an important property: it maps directly to the first 256 Unicode codepoints (by construction, since Unicode was designed so that property was true). This means that converting from ISO 8859-1 to UCS-2 or UTF-16 is a simple zero-extension. That has direct performance benefits when doing any operation which mixes ISO 8859-1 and UCS-2 or UTF-16, which will happen often if the internal representation for String can use either. For instance, searching for an ASCII substring within a long UTF-16 string (ASCII maps directly to the first 128 ISO 8859-1 values, another important property).

Yes, it's not the most minimal representation, but since Strings are so common in Java, performance is important. And a lot of Strings use only the first 256 codepoints. It's mentioned in the linked article: "Data gathered from many different applications indicates that strings are a major component of heap usage and, moreover, that most String objects contain only Latin-1 characters."

...but, if I've understood the proposal correctly, the public interface isn't changing. The user of String will never know, nor care, whether their string is implemented as UTF-8 or ISO-8859-1. This is purely an implementation detail.

Personally, I'd be astonished if JVMs didn't already do this: way back when when I was working for a company that did embedded JVMs, it was one of the first optimisations we did. When class files were loaded, we'd look at each string, and if they were ISO-8859-1 we'd use a byte-based representation rather than a word-based one. (Programmatically created strings were always words, of course.)

Even in an environment where most of our customers were Asian the savings were huge. Java uses a lot of identifier strings.

ISO 8859-1 does have the unique property that each of its 256 code points map directly to the first 256 Unicode code points.

Firefox did this recently, with great success. It's a simple solution that will reduce memory usage (and this, garbage collection). It makes perfect sense.

HTML is ISO 8859-1 by default, which privileges that legacy encoding within conformant browsers and web servers. That's the reason for all the "character entity" stuff.

The same is not true of Java.

No longer true, HTML5 is UTF8 by default.

HTML is a locale specific encoding by default. (No, really.) Most locales default to windows-1252, not ISO-8859-1.

That said, all conforming HTML documents must now use UTF-8.

Why is this even being discussed? It's only an implementation optimization, no change to the language interface. I don't recall such a fuss around compressed pointers. This is so much better than the number of software stacks that introduce ByteString types specifically for this benefit. If String just did this when it could, then it could just be knowingly used in place of each roll your own.