How to reverse char[]?

[Jonathan M Davis]

On Wednesday, February 08, 2012 17:52:17 Manfred Nowak wrote:
> Jonathan M Davis wrote:
> > thanks to how unicode works
> 
> This does not mean, that the data structure representing a sequence of
> "letters" has to follow exactly the "working" you cited above. That
> data structure must only enable it efficiently. If a requirement for
> sequences of letters is, that a sequence `s' of letters indexed by some
> natural number `n' gives the letter `s[n]' and that is not efficiently
> possible, than unicode and its "workings" are as maldesigned as the
> alphabet Gutenberg has to take to produce books:
> 
> take randomly an ancient book `b' and randomly a letter `c'. Then try
> to verify that `b[ 314.159] == c'. Of course you are allowed to read
> only one letter.

It is impossible to have a random access range of characters with unicode 
unless you have a range of graphemes - which would require a grapheme to be a 
struct of some kind which represented a character - either that or an array of 
arrays. So, you could have

char[][]

where each char[] is a grapheme. But as long as you're dealing with an array 
of code units or code points like we do now, it's impossible to have efficient 
random access of characters. Phobos currently takes the tact of treating a 
code point as a character, which _mostly_ works, but it's not correct.

And while unicode could definitely have been designed better IMHO (e.g. forcing 
code point order with modifying code points and _not_ having multiple ways to 
generate the same character), the core problem is that you're forced to have 
variable length encodings. It wouldn't be feasible to have an integral value 
which represented _every_ single character, because of the combinatorial 
explosion caused by code points which modify other code points (e.g. 
subscript, superscript, cedille, etc.). So, there are problems which are just 
integral to the issue of designing unicode and which cannot be avoided no 
matter how good a job you do at designing unicode. And, of course, there are 
issues with the design on top of that.

- Jonathan M Davis