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Thread overview
My idea for seamless interop to C++
Nov 18
Markus
Nov 18
jmh530
Nov 18
Markus
6 days ago
Jacob Carlborg
6 days ago
Jacob Carlborg
6 days ago
Jacob Carlborg
6 days ago
Atila Neves
6 days ago
jmh530
4 days ago
Atila Neves
6 days ago
Markus
6 days ago
Markus
November 18
Hi there!

For months I've been thinking on how to escape C++.
Here are my thoughts about that matter:
https://gitlab.com/qwertzui11/d-to-cpp/-/blob/master/README.md

What do think about that idea. Is it worth a shot? I'm thinking about implementing such a tool.

Have fun,
Markus
November 18
On Wednesday, 18 November 2020 at 14:04:36 UTC, Markus wrote:
> Hi there!
>
> For months I've been thinking on how to escape C++.
> Here are my thoughts about that matter:
> https://gitlab.com/qwertzui11/d-to-cpp/-/blob/master/README.md
>
> What do think about that idea. Is it worth a shot? I'm thinking about implementing such a tool.
>
> Have fun,
> Markus

I think I'm missing a few steps.

How does this line work
fun->doFunStuff();
if MarkdownToHtmlImpl only inherits from MarkdownToHtml and not FunUseCase?

Wouldn't you want to make a FunUseCase that has MarkdownToHtmlImpl (or MarkdownToHtml) as a member?
November 18
On Wednesday, 18 November 2020 at 15:10:53 UTC, jmh530 wrote:
> On Wednesday, 18 November 2020 at 14:04:36 UTC, Markus wrote:
> How does this line work
> fun->doFunStuff();
> if MarkdownToHtmlImpl only inherits from MarkdownToHtml and not FunUseCase?
>
> Wouldn't you want to make a FunUseCase that has MarkdownToHtmlImpl (or MarkdownToHtml) as a member?

You are completly right. I failed in the example. I fixed it.

It should of course look like this

```cpp
int main(int, char *[]) {
  std::shared_ptr<MarkdownToHtml> converter =
      std::make_shared<MarkdownToHtmlImpl>();
  std::shared_ptr<FunUseCase> fun = FunUseCase.create(converter);
  fun->doFunStuff();
  return 0;
}
```

6 days ago
On Wednesday, 18 November 2020 at 14:04:36 UTC, Markus wrote:
> Hi there!
>
> For months I've been thinking on how to escape C++.
> Here are my thoughts about that matter:
> https://gitlab.com/qwertzui11/d-to-cpp/-/blob/master/README.md
>
> What do think about that idea. Is it worth a shot? I'm thinking about implementing such a tool.
>
> Have fun,
> Markus

Kudos for the detailed comparison between the different C++ alternatives!

That said, I'm sorry to disappoint, but I don't think this would be a a viable approach (translating D source code to C++ (not just headers) while preserving the high-level structure). D is also a complex language (just the complexity is much less and much better managed compared to C++) and doing a semantically correct translation (while even preserving high-level concepts, such as OOP) would be quite hard. D's template system is more powerful (and more sane) than the one of C++, so you can't translate any D code that use templates basically (which is pretty much the whole standard and runtime library).

I believe there are 5 approaches / areas worth investing to:
1. dmd's built-in extern (C/C++) ABI and header generation [1] [6] [7] [8]
2. dpp [2]
3. dstep [3] (I really wish Atilla would collaborate with Jacob on merging dpp and dstep)
4. cling [4] - as far as I know Symmetry have build some sort of bridge between D and C++ based on this.
5. Calypso - using Qt from D is nothing sort of astonishing! Unfortunately all the work is done by single developer. If others would join, hopefully the project could progress much faster.

[1]: https://dlang.org/changelog/2.091.0.html#headers
[2]: https://github.com/atilaneves/dpp
[3]: https://github.com/jacob-carlborg
[4]: https://github.com/root-project/cling
[5]: https://wiki.dlang.org/Calypso

[6]: https://dlang.org/changelog/pending.html#dtoh-improvements | permalink: https://github.com/dlang/dmd/blob/82cbfec6c72a5ece1b2a9a72d18adcae145d10c7/changelog/dtoh-improvements.dd
[7]: https://dlang.org/changelog/2.094.0.html#cxx-header-modes
[8]: https://dlang.org/changelog/2.092.0.html#cpp_abi_tags

I'm curious to know more on your thoughts on dmd's dtoh.

You can find some sample generated code here:

Big example:
https://github.com/MoonlightSentinel/dmd/blob/ecce5075cbdef1e41b502ccfc01d188ecce4ebc6/src/dmd/frontend.h

Smaller examples:
https://github.com/MoonlightSentinel/dmd/blob/72e5188bd66e4bd8b23f12f0979d66e8354c7d2a/test/compilable/dtoh_cpp98_compat.d

https://github.com/MoonlightSentinel/dmd/blob/72e5188bd66e4bd8b23f12f0979d66e8354c7d2a/test/compilable/dtoh_enum.d

https://github.com/MoonlightSentinel/dmd/blob/72e5188bd66e4bd8b23f12f0979d66e8354c7d2a/test/compilable/dtoh_extern_type.d

https://github.com/MoonlightSentinel/dmd/blob/72e5188bd66e4bd8b23f12f0979d66e8354c7d2a/test/compilable/dtoh_functions.d

6 days ago
On Wednesday, 18 November 2020 at 23:32:00 UTC, Petar Kirov [ZombineDev] wrote:

> 5. Calypso - using Qt from D is nothing sort of astonishing! Unfortunately all the work is done by single developer. If others would join, hopefully the project could progress much faster.

As far as I recall, this is using libclang built-in into LDC. This would limit the usage to LDC.

> [3]: https://github.com/jacob-carlborg

Correction: https://github.com/jacob-carlborg/dstep

--
/Jacob Carlborg

6 days ago
On Thursday, 19 November 2020 at 07:02:58 UTC, Jacob Carlborg wrote:
> On Wednesday, 18 November 2020 at 23:32:00 UTC, Petar Kirov [ZombineDev] wrote:
>
>> 5. Calypso - using Qt from D is nothing sort of astonishing! Unfortunately all the work is done by single developer. If others would join, hopefully the project could progress much faster.
>
> As far as I recall, this is using libclang built-in into LDC. This would limit the usage to LDC.

Yes, this project is completely tied to LDC. However, it is the one also offering the tightest C++-interop (except for the cling-based approach, for which idk - a dconf presentation would be nice). The integration has several noticeable advantages:
1. It is using the C++-based libclang API, which from what I've heard offers much more than the C wrapper-based one.
2. I don't know the specifics, but AFAIR, the integration point is not actually the parsed AST, but actually more closer to the mid-layer, so it has much more semantic information and doesn't need to use D's extern (C++) support (though that certainly helps), as it can do things on the Clang/LLVM-level.
3. It deeply integrates also with DMDFE in order to bridge the clang AST and the DMD AST and even makes additions to D itself, in order to enable things like C++ overload resolution.
(I'm not involved with the project, so I may be misremembering or misrepresenting some details, but that's some of the high-level stuff, AFAIR.)

Unfortunately, 1. and 2. are also the project's biggest weakness (given the available man power), as C++ clang, LLVM and DMDFE APIs are pretty unstable, so I guess it requires extensive effort to rebase to the latest versions.

>
>> [3]: https://github.com/jacob-carlborg
>
> Correction: https://github.com/jacob-carlborg/dstep

Sorry for the typo.

dpp makes for some cool live demoes, but I've always preferred my source code committed to git, rather than just existing in-memory (well unless it's well-written CTFE code :D), so dstep has been my preferred choice for C HtoD. Huge thank you for it! :)

6 days ago
On Thursday, 19 November 2020 at 07:37:52 UTC, Petar Kirov [ZombineDev] wrote:

> Sorry for the typo.

No worries :)

> dpp makes for some cool live demoes, but I've always preferred my source code committed to git, rather than just existing in-memory (well unless it's well-written CTFE code :D), so dstep has been my preferred choice for C HtoD. Huge thank you for it! :)

You're welcome. Thanks for those kind words.

--
/Jacob Carlborg
6 days ago
On Thursday, 19 November 2020 at 07:37:52 UTC, Petar Kirov [ZombineDev] wrote:

> Yes, this project is completely tied to LDC. However, it is the one also offering the tightest C++-interop

A side note: looks like Swift is planning for C++ interoperability [1]. For the C the interoperability, Swift uses the same approach as Calypso. Zig does this as well [2].

[1] https://github.com/apple/swift/blob/main/docs/CppInteroperabilityManifesto.md
[2] https://ziglang.org/#Integration-with-C-libraries-without-FFIbindings

--
/Jacob Carlborg

6 days ago
Thx for your great reply!

On Wednesday, 18 November 2020 at 23:32:00 UTC, Petar Kirov [ZombineDev] wrote:
> That said, I'm sorry to disappoint, but I don't think this would be a a viable approach (translating D source code to C++ (not just headers) while preserving the high-level structure). D is also a complex language (just the complexity is much less and much better managed compared to C++) and doing a semantically correct translation (while even preserving high-level concepts, such as OOP) would be quite hard. D's template system is more powerful (and more sane) than the one of C++, so you can't translate any D code that use templates basically (which is pretty much the whole standard and runtime library).

I completely agree! D-templates are complex, but unlike in C++ manageable. However I'd simply not support them :) It shall not be possible to instance a D-template in C++. Keep it simple and usable! In the end of the day, that's one thing that makes D so awesome. D is not C++ compatible. However I'd like D to be compatible with a sane simple subversion of C++. Which is the exchange of build-in-types.
So the interop shall ONLY support build-in types, combinations of them (`struct`/POD) and non-templated classes. functions and methods shall only take and return build-in-types/POD.
In my opinion that's all that's needed for D to work cleanly and safe with C++. Everything else would require "magic".
A module shall have a simple interface. That should do for 99% of all the cases. This way it would be easily possible to access the vast ecosystem of C++. The D-UseCase provides an Interface of what it wants, and in C++ you implement that interface to a library/framework of your choosing.

So in my opinion, with that subversion of D and C++ a seamless interop should be possible and quite helpful. Could I change your mind?

> I believe there are 5 approaches / areas worth investing to:
> 1. dmd's built-in extern (C/C++) ABI and header generation [1] [6] [7] [8]

I really like the direction this dtoh is going. And thanks for the link to the upcoming version, I did not read that one before. I tested it, and what I didn't like is that it generates code like:

```cpp
virtual void setString(DArray< char > ) = 0;
virtual SomeClass* getSomeClass() = 0;
```

You get raw pointers and custom arrays. I get it why they are doing it like that. It's the fastest and most flexible solution.
However, it includes manual memory management, it's unsafe and you still have to write an error-prone glue code. In example of the string, I'm sure in a real world project you will cast `DArray<char>` to `std::string` and vice-versa. Why not do it for them, when generating the wrapper. Out of the box awesomness :D and more concentration on the problem, not on the language and its interfacing.

> 2. dpp [2]

Great tool, until C++ gets involved. Epic for C! no doubt.

> 3. dstep [3] (I really wish Atilla would collaborate with Jacob on merging dpp and dstep)

Great tool too... for C.

> 4. cling [4] - as far as I know Symmetry have build some sort of bridge between D and C++ based on this.
> 5. Calypso - using Qt from D is nothing sort of astonishing!

these are C++ to D tools? not D to C++?
Calypso really looks astonishing. will give it a try!

Have fun
Markus
6 days ago
On Wednesday, 18 November 2020 at 23:32:00 UTC, Petar Kirov [ZombineDev] wrote:
> On Wednesday, 18 November 2020 at 14:04:36 UTC, Markus wrote:
>> [...]
>
> I'm curious to know more on your thoughts on dmd's dtoh.
>
> [...]

looks like I messed up the "reply" function in this old-school forum. My answer to your post is here:
https://forum.dlang.org/post/ymmmhvnmmhfgajhziikd@forum.dlang.org
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