C++ interop
Timothee Cour via Digitalmars-d
digitalmars-d at puremagic.com
Mon Jan 30 19:36:11 PST 2017
also: catch D exceptions from C++ vs catching C++ exceptions from D; IIRC
only one direction is supported
On Mon, Jan 30, 2017 at 11:42 AM, kinke via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:
> I was wondering whether C++ interop is already considered sufficiently
> working enough, as I don't see any plans for improving it in the H1 2017
> vision, except for the `C++ stdlib interface` bullet point.
>
> IMO, the main obstacles for mixed D/C++ RAII-style code are:
>
> 1) Constructors don't work across the C++/D language barrier, as they are
> mangled differently and slightly differ in semantics (D ctors assume the
> instance is pre-initialized with T.init) => currently need to implement
> them on both sides. Additionally, D structs cannot have a non-disabled
> parameter-less constructor.
> 2) Destructors need to be implemented on both sides as well.
> 3) Copy/move constructors/assignment operators too.
>
> I think D could do a lot better. Constructors for example:
>
> // D
> extern(C++) struct T {
> this(bool a); // declares C++ ctor T::T(bool)
>
> extern(D) this(int a)
> {
> // Generates D ctor T::__ctor(int) and C++ ctor T::T(int).
> // The C++ ctor is implemented as `{ this = T.init; this.__ctor(a); }`
> // to initialize the memory allocated by C++ callers.
> // D clients call the D __ctor directly to avoid double-initialization;
> // that's what the extern(D) makes explicit.
> }
> }
>
> // C++
> struct T {
> T(bool a) {
> // Callable from D; instance will be initialized twice then.
> }
>
> T(int a); // declares the C++ ctor wrapper emitted by the D compiler
> };
>
> Similarly, the D compiler could generate explicit C++ copy and move
> constructors automatically if the extern(C++) struct has an extern(D)
> postblit ctor, so that C++ clients only need to declare them. `extern(C++)
> this(this);` postblit ctor declarations could be used to make D clients
> call copy/move ctors implemented in C++ etc...
>
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