Julian Salazar wrote:
Hi, I'm new here to the community but I've been using D for a while now,
and I have to say that it's a great programming language. I'd like to
get involved in this community and help shape this language.
Welcome!
I'm just wondering about a minor issue: why are conditional blocks
invalid within expressions such as enum and asm? I mean, in trivial
cases it's fine, but in instances where code duplication is a big
maintainability nightmare, making conditional compilation more flexible
would have benefits for developers.
The request to do it for enums has been thrashed about before.
Essentially, version works at the declaration and statement level, not
at the expression level or in between tokens, etc. The reason for this
is to encourage a more modular approach to versioning than the typical C
method of doing it at the lowest level.
Something like (I know it's a trivial example, but you get the point):
asm {
version(x86) mov EAX, 1;
else version(x86_64) mov EAX, 2;
}
would trigger an error. Also, though I know enum qualifies as a
constant/datatype cross, structs and classes are perfectly fine with
conditional compilation. Couldn't the lexical stuff be changed to
support it for enum and asm as well?
Let me illustrate by a current example. The linker (optlink) is written
100% in assembler. This makes it rather intractable. It's also loaded up
with line-by-line nested conditional assembly (and a lot of macros).
It's so hard to see what is *actually* being compiled that I'll assemble
it, run OBJ2ASM on the output, and work off of the disassembled code.
So, in essence, the idea is to push conditional compilation to higher
levels, not lower levels. Ideally, versioning would be done by
abstracting all the version differences into an interface implemented by
different modules.
Also, I noticed that there is no formal specification page for x86-64
inline assembly. You define a predefined version identifier such as
D_InlineAsm_X86_64, but you don't define registers and instructions
pertaining to it. In GDC for example, using the RAX register in the D
inline ASM syntax is invalid. Not sure what the case is in LDC (they
probably do implement it for x86-64), and I know DMD does not have a
64-bit version, but the spec should at least have a definition for
compilers that do implement 64-bit support.
The first approximation to the definition is to use the Intel asm syntax
as outlined in their processor data sheets. I haven't written a spec
more detailed than that because it's a lot of work and I'm lazy, and
such work is not terribly exciting. But if you'd like to help with that,
I'd welcome it.
