Generally Linux systems use UTF-8 so I guess the "system
encoding" there will be UTF-8. But then if you start to use
QT you have to use UTF-16, but you might have to intermix
UTF-8 to work with other libraries in the backend (libraries
which are not necessarily D libraries, nor system
libraries). So you may have a UTF-8 backend (such as the
MySQL library), UTF-8 "system encoding" glue code, and
UTF-16 GUI code (QT). That might be a good or a bad choice,
depending on various factors, such as whether the glue code
send more strings to the backend or the GUI.
Now try to port the thing to Windows where you define the
"system encoding" as UTF-16. Now you still have the same
UTF-8 backend, and the same UTF-16 GUI code, but for some
reason you're changing the glue code in the middle to
UTF-16? Sure, it can be made to work, but all the string
conversions will start to happen elsewhere, which may change
the performance characteristics and add some potential for
bugs, and all this for no real reason.
The problem is that what you call "system encoding" is only
the encoding used by the system frameworks. It is relevant
when working with the system frameworks, but when you're
working with any other API, you'll probably want to use the
same character type as that API does, not necessarily the
"system encoding". Not all programs are based on extensive
use of the system frameworks. In some situations you'll want
to use UTF-16 on Linux, or UTF-8 on Windows, because you're
dealing with libraries that expect that (QT, MySQL).
Agreed. True, system encoding is not always that clear. Yet, usually UTF-8 is
common for Linux (consider also Gtk, wxWidgets, system calls, etc.) At the same
time, UTF-16 is more common for Windows (consider win32api, DFL, system calls,
etc.). Some programs written in C even tend to have their own 'tchar' so that
they can be compiled differently depending on platform.
A compiler switch is a poor choice there, because you can't
mix libraries compiled with a different compiler switches
when that switch changes the default character type.
Compiler switch is only necessary for system programmer. For instance, gcc also
has 'fshort-wchar' that changes width of wchar_t to 16 bit. It also DOES break
the code casue libraries normally compiled for wchar_t to 32 bit. Again, it's
generally not for application programmer.
In most cases, it's much better in my opinion if the
programmer just uses the same character type as one of the
libraries it uses, stick to that, and is aware of what he's
doing. If someone really want to deal with the complexity of
Programmer should not know generally what encoding he works with. For both
UTF-8 and UTF-16, it's easy to determine number of bytes (words) in multibyte
(word) sequence by just looking at first code point. This can also be builtin
function (e.g. numberOfChars(tchar firstChar)). Size of each element can easily
be determined by sizeof. Conversion to UTF-32 and back can be done very
transparently.
The only problem it might cause - bindings with other libraries (but in this
case you can just use fromUTFxx and toUTFxx; you do this conversion anyway).
Also, transferring data over the network - again you can just stick to a
particular encoding (for network and files, UTF-8 is better since it's byte
order free).
supporting both character types depending on the environment
it runs on, it's easy to create a "tchar" and "tstring"
alias that depends on whether it's Windows or Linux, or on a
custom version flag from a compiler switch, but that'll be
his choice and his responsibility to make everything work.
If it's a choice of programmer, then almost all advantages of tchar are lost.
It's like garbage collector - if used by everybody, you can expect advantages
of using it. However, if it's optional - everybody will write libraries
assuming no GC is available, thus - almost all performance advantages are lost.
And after all, one of the goals of D (if I am not wrong) to be flexible, so
that performance gains will be available for particular configurations if they
can be achieved (it's fully compiled language). It does not stick to something
particular and say 'you must use UTF-8' or 'you must use UTF-16'.
michel.for...@michelf.com
http://michelf.com/
