explain @cfunction in Embedding Julia manual

[stevengj]

For people wanting to call Julia from C/C++, I would generally recommend doing all of the type conversions on the Julia side, and then use jl_unbox_voidpointer(jl_eval_string("@cfunction(....)")) to compile and extract a C function pointer that you can then call normally. This is vastly easier than constructing/unboxing Julia types from the C/C++ side.

It would be good to document this in the Embedding Julia manual, which currently doesn't mention @cfunction at all.

(For example, this came up on stackoverflow in a question about calling the Julia SpecialFunctions.polygamma function from C++.)

[pemryan]

I also figured a way to call julia functions in C++ via jl_function_ptr:
https://discourse.julialang.org/t/calling-julia-functions-using-cfunction/9032

[danilo-bc]

Bumping this thread because it's still relevant, specially with some welcome changes in Julia 1.6 and 1.7

[mhnsn]

Bumping this thread also, because serious support and documentation for C/C++ integration with Julia would be game-changing for next-generation Edge AI applications.