I'm still struggling with this.
Felix has a couple of ways to deal with it.
1. Conditional code generation: lib/plat.
Done at config time.
2. C++ conditional stuff. Eg async I/O, pthreads etc.
3. Felix conditional compilation. This is used in Faio
at the moment.
4. Abstraction by virtual functions.
This is "apparently" nice. You can compile both windows and
unix code instances, and just select one using a dummy type.
But dummy types suck. Also, this only handles functions
common to all platforms. It doesn't handle, say, rejection
of platform dependent code, or, using say an XSI function
on a non-XSI posix platform.
There's a need to think. First, Felix code SHOULD be able to
generate either Unix or Windows code, no matter what the
host is. The target could be otherwise: we don't have to compile
the generated C++ on the platform that generates it.
AHHHH .... Eureka...
C++ with conditional compilation is how Felix makes portable RTL
code.
So the right way to write "platform independent" code is NOT
conditional compilation in Felix .. but conditional compilation
in C++ .. GENERATED BY FELIX.
In other words instead of
proc f() {
if windows do
windows_f();
else
posix_f()
done
}
which generates code for either windows or posix, we should
be generating this:
proc f() {
hash_ifdef_windows();
windows_f();
hash_else();
posix_f();
hash_endif();
}
which generates:
void f() {
#ifdef WINDOWS
C_windows_f();
#else
C_posix_f();
#endif
}
so the conditional testing is done at C++ compile time.
Of course this won't play with requirements for header files,
since both windows and posix headers needed by the C
functions will be included, so we need to #ifdef them too.
Of course the syntax above is only a demo that will work
right now (not real syntax for this feature).
The above Felix generates a "universal source" sort of like
Apples universal binaries.
Of course it won't "properly" work as written because Felix
generates, say, functions, in pieces:
struct f_type;
...
struct f;
..
struct f : f_type{ ... };
void f::call();
etc. So really we want to tag the code "for windows" so all the parts
of the function as above get conditionals around them .. hmmm ...
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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