Proof of Concept: Binding to and extending C++ objects via a metric fuckton of templates

[dsimcha]

== Quote from downs (default_357-line at yahoo.de)'s article
> I've just committed a module to tools (tools.cpp,
http://dsource.org/projects/scrapple/Trunk/tools/tools/cpp.d ) that should enable
linking and using any C++ library with D programs without creating a C wrapper for it.
> The code has been tested with a simple multiple-inheritance sample:
http://paste.dprogramming.com/dpv8hpjp
> The D code to bind to this is http://paste.dprogramming.com/dphlv1ot . It
requires a symlink to the tools folder in its directory.
> Caveats:
>  - D1
>  - Only works on g++4's "newapi" layout and mangling (but should be reasonably
portable).
>  - Diamond pattern is untested and unsupported.
>  - Class protection is completely unsupported - public only.
>  - RTTI must be generated manually (normally the compiler would do this). See
the D half of the sample.
>  - Dynamic casting from and to generated classes is not implemented.
>    - The C++ code that does this is long and full of special cases, so
>    - For the example, I ended up hardcoding a manual translation between A and B.
>    - If you need dynamic casting, I recommend hardcoding the required paths
based on classinfo pointer comparisons.
>  - The C++ DSL parser is not very tested. Occasional bugs may occur.
>  - When building with LDC, fixup_vtable() needs to be called for every newly
created C++ class object.
>    - This is because LDC does not yet support initialization from global
variable addresses.
> Building the sample is a two-step process:
> g++ test.cpp -c -g -o test.o
> gdc -J. cpp_demo.d tools/cpp.d tools/base.d tools/smart_import.d tools/ctfe.d
tools/compat.d tools/text.d tools/tests.d tools/log.d test.o \
> 	-o cpptest -lstdc++ -L /usr/lib/gcc/i686-pc-linux-gnu/4.3.2/ -g # adapt library
path as appropriate
> Writing this also gave us what I believe to be a fair contender to Most
Horrifying Statement of D Ever Written:
>   fndefs ~= `mixin("extern(C) `~t~` "~`~mname~`~"`~fnparams~`; ");`~'\n'~
>       `mixin("`~fn~`("~refToParamList("Params!(typeof(&"~`~mname~`~"))",
isRef!(typeof(mixin("&"~`~mname~`))))~") {
>       return
"~`~mname~`~"("~refToValueList(isRef!(typeof(mixin("&"~`~mname~`))))~");
>     }
>   "); `;
>  --downs

Awesome!  One quick question.  This may be a stupid question, as I don't
understand at all yet how this works:  Can you instantiate C++ templates with this
thing, or does it work only w/ non-templated C++ code?