Advocacy (Was: Who here actually uses D?)

[Walter Bright]

bearophile wrote:
> Walter:
> 
>> Based on what?
> 
> It's just a lump of opinions of mine, I have not written a microkernel yet
> :-) But I am reading a lot, I am learning and I will be able to write this
> kind of code too.
> 
> Some people have tried to write a kernel with Python. D2 is a nice language
> to use, it allows some low level control, inline asm, and it compilation
> model comes from C with things added. So I am sure it's possible to write a
> good enough kernel with D2. So it's a matter of how much the language is fit
> for this purpose, it's not a binary thing. Is D2 the best conceivable
> language to write a kernel? I don't think so (but I am often wrong).

It's not perfect, but it is better than any other existing language.


> For a kernel writer D2 doesn't offer a lot of control on low level matters,
> like how the compiler compiles and optimizes code (see the thread about
> "guaranteed optimizations".

I'm afraid that's baloney, as I pointed out in the other thread.


> This is a case where you don't want to "Let the
> compiler implementors do their job" because you lose low-level control on the
> code produced and this introduces bugs). This was one of the main complaints
> of Linus against C++ for Linux kernel development.

I think that is a serious misinterpretation of the complaint. The complaint was 
actually that the high level abstractions that one can choose to use in C++ can 
be impenetrable in what they do. In D, if you want low level control, write low 
level code. It's that simple.


> D2 type system is refined and much more powerful than the C one. And people
> have written many kernels with C (C plus with few nonstandard extensions).
> But if you want to write a modern kernel you may want a type system more
> powerful than the C and D ones, that give stronger static guarantees. Linus
> has written a tool to strengthen the C type system: 
> http://en.wikipedia.org/wiki/Sparse

Yes, I know about Sparse. You can do the same thing in D without needing 
annotations.

> In another thread I have written
> something about typed assembly, useful to make less wild parts written in
> assembly: 
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=125815
>  In some situations linear types too help: 
> http://en.wikipedia.org/wiki/Linear_types

Typed assembler is a waste of effort in a language like D, as you only need a 
few drops of assembler here and there.

> The Spec# language and the
> experimental Verve kernel we have discussed a bit in past show possible
> directions for future kernels, they require a pretty strong static analysis.

Those languages are failures at what they propose to do; they need years and 
perhaps decades to fulfill that.

> The Sparse tool shows that some of those type system feature may be added
> later to D with an external tool.

Like I said, you can already do that with D.

> But Verve shows that sometimes you need something more built-in.

I don't buy that.