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

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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~`))))~");
    }
  "); `;

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