D vs C++ classes?

[Ola Fosheim Grøstad]

On Wednesday, 30 June 2021 at 10:38:36 UTC, Alexandru Ermicioi 
wrote:
> On Wednesday, 30 June 2021 at 09:53:31 UTC, Ola Fosheim Grøstad 
> wrote:
> If you open object.d and check for TypeInfo symbols you'll 
> notice that they are final classes. We should replace them with 
> a set of interfaces (with nice names without uncompliant 
> underscores by code style standards), and then let d compiler 
> generate an implementation for each class it has compiled.

Do you mean using a function call to obtain specific type info?

> If you want full 100% interop, just use c++. There is bound to 
> be shortcomings in interoperability, and imho we should not 
> sacrifice the language, just for that. If this will be the 
> future orientation for D I don't see the point of it having 
> letter D, let's just rename it to C++++

Runtime compatibility does not equate compile time limitations, 
so it isn't really all that limiting given the current D 
semantics. The difference between D and C++ on the compile time 
level isn't really touched.

> 1. My suggestion of allowing to express multiple inheritance, 
> was for c++ class declarations only, i.e. class header files 
> only.
> 2. Making them compatible with C++ abi doesn't imply that they 
> are c++ classes, and hence should support all c++ features. 
> They are still D classes or a subset of them that can be called 
> by c++ code.

You need to be able to specialize C++ classes in order to have 
full C++ library interop. So it is a given requirement that you 
need to be able to declare/define/instantiate extensions of C++ 
classes in D, in order to have basic C++ interop.

> Let's not conflate two distinct domain objects into one. There 
> is a class that is written in D, and there is one written in 
> C++, they are not the same thing.

You need to be able to extend the one in C++ from D in order to 
integrate, so it basically is the same thing.

Most modern C++ libraries are also heavily templated so to have 
basic interop you actually need to translate D code to C++.

That is, if C++ interop is a goal. Most people don't want 50% 
interop they expect close to 99% interop. If only 50% is the 
goal, then maybe just stick to C interop and forget about C++, 
most people don't care for 50% anyway.

> Let's also clarify what full interoperability means. Per my
> understanding, this means that I can use all of libs written in
> c++, and then I can expose my D code to the c++ libs and allow
> them use it, but it does not mean, that I need to follow the
> c++ rules for the oop, or any other feature, otherwise, why not
> replace D lambdas, with std::function from c++? We need full
> interoperability...

std::function is just a buffer, but yes, D does need something 
comparable although in C++ std::function is a last resort, you 
would typically use a template instead.