Unicode guide

This is a WIP page, take nothing here as final.

Introduction

Over the past decade it's been increasingly common to see programming languages add Unicode support: Specifically, support for Unicode strings. This is a good step, but it's not nearly complete and often done in a buggy way. Hopefully in this page I can show what's wrong with this approach and provide some solutions.

Just to make it clear: Unicode is only a part of a complete localization framework. Languages do a bunch of other things wrong, but broken Unicode string handling is the topic I'm covering in this page.

Unicode refresher

If you don't understand what Unicode is, I highly recommend reading the following resources in this order:

1. The Unicode Standard, Version 14.0 chapters 1, 2, 3, 4, 5 and 23
2. Unicode Technical Reports
3. Unicode Frequently Asked Questions

You might also find the following tools helpful:

• Unicode Utilities
• Unicode Code Charts

But as a general overview, Unicode defines the following:

• A large multilingual set of abstract characters
• A database of properties for each character (this includes case mapping)
• How to encode characters for storage
• How to normalize text for comparison
• How to segment text in to characters, words and sentences
• How to break text in to lines
• How to order text for sorting

Some of these can be tailored by locale-dependant rules. The Unicode Common Locale Data Repository provides locale-specific information that aids in this tailoring.

ASCII strings

- encoding-neutral but really it's ascii

- character set

- strings

- ops

- OS APIs provide strings

- simple, english based

- works with ascii-compatible encodings

- you don't have to learn anything complicated

Unicode strings

- utf-8

- OS APIs

- string APIs make less sense

- locale tagging

- utf8b

- bytestrings

- poorly defined semantics

ICU strings

ICU/Java?

Non-destructive text processing

- clear, unicode definitions

- rich text

- multiple versions

- metadata

- non-reversible