a lua upvalue can be lightuserdata, userdata, or anything else that can have its address taken (it's immediately popped of the stack and carted around with function call)
a lightuserdata can only be a pointer (void*)
a regular userdata can be anything, but is stored as void* because of "anything" semantics and C heritage of lua
upvalues deserve to use the `lua_upvalueindex(n)` macro: lightuserdata/userdata does not (must not) go through this process
get turned into getter<T>, matches pusher<T> and uses same semantics as std::allocator and other things used throughout the codebase
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userdata has its traits defined outside in new file of userdata to prevent errors when trying to use those typetraits in places before userdata.hpp gets included
userdata was changed to support returning itself via pointers or references.
rework of stack changes semantics based on T&, T*, and T&& (the last one tries to create a new userdata and move in data)
solves problems maybe presented in https://github.com/Rapptz/sol/issues/25
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container.hpp is attempt at solving original problem before going on wild tangent with userdata, stack, and get
is going to attempt to use userdata to allow transporation of containers losslessly, perhaps without copying need
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found out trying to return a std::function does not work -- not sure what do exactly?
perhaps should push c closure as last thing, but right now it is tied to a key value (code comes from table.hpp and set_function)
will just have to think over how stack arranges itself and learn what to do
by forward-declaring the std::function overload in `stack`, it is able to find the right function to use.
All tests are passing
the ninja file has been tweaked to make it easier to invoke a g++ build on windows
tests added to confirm userdata can be passed into C++ function types
demangle is now named lua_demangle, and the core demangle without any replacements (to fit lua) is just named demangle
Formattings fixes everywhere
Fix for userdata to accept base classes where the derived class uses the name of a base member function to access it (Derived::get_num, where get_num is only implemented in Base::get_num)
VC++ makes this acceptance easy by taking the name as "Derived", but GCC and Clang
