C++ support keeps coming up these days, with Andrei continually stressing it as something to work on.  How hard would it to be to write a C++->D translator, to allow people to translate C++ libraries to D?

I've been using tools like DStep and looking at libdparse, which seem to work very well.  I just translated a C sample app from the Android NDK to D, fairly simple stuff like turning -> into ., adding a default in a switch statement, rewriting casts from C-style to D-style casts, removing the struct label, nothing that couldn't be automated.

I'm sure there's stuff that'd need to be done by hand, but if you can automate 97%, that's good enough.  Could this be a viable option for many cases?

On Thu, 21 Aug 2014 06:35:53 +0000
Joakim via Digitalmars-d <digitalmars-d@puremagic.com> wrote:

i believe that all code that using STL/Boost will not be translated (and this is the majority of C++ code, i think). and only very-very primitive templates can be translated automatically.

so maybe i'm not right, but i think that automatic translation can do something about 3% of existing code. ;-)

On 21/08/14 08:35, Joakim wrote:
> C++ support keeps coming up these days, with Andrei continually
> stressing it as something to work on.  How hard would it to be to write
> a C++->D translator, to allow people to translate C++ libraries to D?
>
> I've been using tools like DStep and looking at libdparse, which seem to
> work very well.  I just translated a C sample app from the Android NDK
> to D, fairly simple stuff like turning -> into ., adding a default in a
> switch statement, rewriting casts from C-style to D-style casts,
> removing the struct label, nothing that couldn't be automated.
>
> I'm sure there's stuff that'd need to be done by hand, but if you can
> automate 97%, that's good enough.  Could this be a viable option for
> many cases?

I think it will be quite difficult. There are probably many cases of C++ code where there is no direct translation in D. libclang, which DStep uses, is probably not enough to do a complete source translation of C++. That means using the C++ Clang API's which are unstable in written in C++.

C is completely different. D was basically designed to allow to easy translate C to D. If a C syntax compiles in D it's supposed to have the same semantics as in C.

It might be possible. As a start you could help out with DStep. Starting to add support for C++ for example.

-- 
/Jacob Carlborg

On 8/20/14, 11:35 PM, Joakim wrote:
> C++ support keeps coming up these days, with Andrei continually
> stressing it as something to work on.  How hard would it to be to write
> a C++->D translator, to allow people to translate C++ libraries to D?
>
> I've been using tools like DStep and looking at libdparse, which seem to
> work very well.  I just translated a C sample app from the Android NDK
> to D, fairly simple stuff like turning -> into ., adding a default in a
> switch statement, rewriting casts from C-style to D-style casts,
> removing the struct label, nothing that couldn't be automated.
>
> I'm sure there's stuff that'd need to be done by hand, but if you can
> automate 97%, that's good enough.  Could this be a viable option for
> many cases?

I think the key here involves clang with hooks + a config file per C++ file to translate that instructs the translator how to proceed about corner cases (e.g. expand this macro but not this other etc). -- Andrei

"Joakim"  wrote in message news:ysntkmioyndreuiiyqxx@forum.dlang.org... 

> C++ support keeps coming up these days, with Andrei continually stressing it as something to work on.  How hard would it to be to write a C++->D translator, to allow people to translate C++ libraries to D?

You might want to look at DDMD, which is automatically converted.

On Thursday, 21 August 2014 at 10:00:43 UTC, Daniel Murphy wrote:
> "Joakim"  wrote in message news:ysntkmioyndreuiiyqxx@forum.dlang.org...
>
>> C++ support keeps coming up these days, with Andrei continually stressing it as something to work on.  How hard would it to be to write a C++->D translator, to allow people to translate C++ libraries to D?
>
> You might want to look at DDMD, which is automatically converted.

Yes, I'm aware of ddmd.  You've mentioned many times that it only works because dmd is written using a very unC++-like style, to the point where github's source analyzer claims that dmd is written in 66.7% C, 28.4% D (presumably the tests right now), 4.4% C++, and 0.5% other. :)

Given tools like libclang, how hard do you think it'd be to translate most of actual C++ to D?  If writing such a tool would mean that C++->D translation is the path of least effort for D users who want to integrate with C++, maybe that's the approach that should be taken instead.

I should note that I have no interest in any C++ libraries: I'm just throwing out this idea as an alternative to all the C++ interfacing that's being considered for D right now.

 Might be pretty hard, C++ has some features D doesn't, not sure how you would emulate them.

C++ has these, I don't think D does:
  move only types
  r-value references
  SFINAE
  ADL
  Multiple inheritance

On Thursday, 21 August 2014 at 17:57:13 UTC, Joakim wrote:
> Yes, I'm aware of ddmd.  You've mentioned many times that it only works because dmd is written using a very unC++-like style, to the point where github's source analyzer claims that dmd is written in 66.7% C, 28.4% D (presumably the tests right now), 4.4% C++, and 0.5% other. :)

That's just because the C++ DMD files have a .c extension. The joke about it being written in C+ is fitting but the source code is pretty easily identified as C++ (if only because it makes frequent use of classes).

On 8/21/2014 10:57 AM, Joakim wrote:
> Given tools like libclang, how hard do you think it'd be to translate most of
> actual C++ to D?

I'd say the possibility of that is about zero. Heck, we can't even do it 100% for C.

The trouble is, D is not a perfect superset of C++, not even close:

1. multiple inheritance
2. SFINAE
3. Koenig lookup
4. tail mutability
5. overloading rules
6. operator overloading rules
7. fwd reference issues
8. macros (it's depressing how much modern C++ practice still heavily depends on the preprocessor)

Does that really matter? In my not-so-humble experience, C++ programmers often, far too often, find some odd corner case in the language and build an entire store on it. I personally find this baffling, but it happens with depressing regularity.

(In contrast, the C++ style used in DMD is very conservative and tends to run right down the middle of the road of C++, avoiding anything clever and corners and weird emergent behavior. This is the only reason why DDMD has even a prayer of working.)

On Thursday, 21 August 2014 at 21:06:09 UTC, Walter Bright wrote:
> On 8/21/2014 10:57 AM, Joakim wrote:
>> Given tools like libclang, how hard do you think it'd be to translate most of
>> actual C++ to D?
>
> I'd say the possibility of that is about zero. Heck, we can't even do it 100% for C.
>
> The trouble is, D is not a perfect superset of C++, not even close:
>
> 1. multiple inheritance
> 2. SFINAE
> 3. Koenig lookup
> 4. tail mutability
> 5. overloading rules
> 6. operator overloading rules
> 7. fwd reference issues
> 8. macros (it's depressing how much modern C++ practice still heavily depends on the preprocessor)
>
> Does that really matter? In my not-so-humble experience, C++ programmers often, far too often, find some odd corner case in the language and build an entire store on it. I personally find this baffling, but it happens with depressing regularity.
>
> (In contrast, the C++ style used in DMD is very conservative and tends to run right down the middle of the road of C++, avoiding anything clever and corners and weird emergent behavior. This is the only reason why DDMD has even a prayer of working.)
OK, you would know better than anyone, thanks for the considered answer.