Re: [boost] [Boost.DLL] Formal Review request

On 3 Oct 2014 at 14:28, Antony Polukhin wrote:

...

Your library could simply be extended to support automatic mangling/demangling for whatever platform you're running it on. All compilers provide functions for demangling (__cxa_demangle, UnDecorateSymbolName/__unDName), however I'm not aware of functions being provided for mangling.

I've tried to do so, but mangling is a very big unsolvable (on a library level) problem. Mangling depends on source code, for example "boost::foo" could be foo function or foo variable. Depending on that knowledge it must be mangled in different ways. More problems arise if foo is an overloaded function that accepts parameters: "boost::foo(variant)". In that case full name of parameter must be specified, which could be boost::variant or variant ...

There was an idea to allow user to forward declare function and generate mangled name from it:

namespace boost { void foo(variant); }

boost::dll::magic_mangle(boost::foo);

But that idea has epic failed... Because of linker problems and no reliable way to get mangled symbol name from compiler internals at compile time. At least I have not found one (any ideas are welcomed).

Both Itanium and MSVC mangling schemes happily have consistent template parameter mangling, so if you wrap the thing you want to mangle like the above and have template<class C> magic_mangle(C &&f) call __func__ or its equivalent to fetch the mangled name of the templated function, extracting the mangled template parameter is a simple string chop. You chop off a fixed length beginning and end, and prepend a little bit of mangling depending on its type of function if it's a function and you should be done. If you remember Antony I sent you a little demo of this back during the review of TypeIndex.

That's why aliases were considered a lesser evil:

BOOST_DLL_ALIAS(boost::foo, foo_variant) // in plugin "foo_variant" // in plugin importer

The neato thing about such mangling generation support is that one can examine, in a natural way, a series of DLLs for the presence of some C++ API. You simply supply the prototype and name of what you want, and it finds it. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/