Calypso: Direct and full interfacing to C++

[Elie Morisse via Digitalmars-d-announce]

On Thursday, 22 January 2015 at 00:08:13 UTC, Walter Bright wrote:
> Just making STL work would be an achievement!
>
> Is the output of Calypso a file that can be imported?

The only outputs specific to Calypso are ligthweight object files 
per C++ module that contain symbols created by LDC for aggregates 
(InitZ...) and template specializations by Clang if they're not 
defined in the PCH.

What Calypso basically does is tell Clang to generate a big PCH 
for all the headers in modmap directives, and to map "on demand" 
C++ declarations from the PCH to D symbols in a separate tree of 
modules (hence the (C++) in imports, they're not physical 
modules). Those symbols can be used like D's, although they have 
different implementations to handle the C++ specificities, and 
all the non-trivial semantic work is done by Clang libraries and 
queried back by Calypso (aggregate layout, partial template 
argument deduction, ...).

There are still some very "feels hackish" areas like the fact 
that DMD considers C++ classes to derive from Object too 
(fortunately Object is only a handful of virtual functions), I 
haven't solved yet how class values should be treated, etc.

Also the PCH is a temporary solution because at the time I began 
working on Calypso Clang's support for modules was broken. But 
they would be great to break the global namespace in smaller 
pieces, so now that they seem ready to use the plan is to replace 
the PCH by them, or by a slightly different flavor of them 
(because there's currently one limitation that reduces its 
usefulness, it's that one header can't be split across several 
modules).