@cfunction for function taking binded class within c++

[k12Sergey]

Hi.
Sorry for silly question, but how to use @cfunction in the foolowing case:
Suppose we bind class:

types.add_type<DataBase>("Database")
   .method("GetProperty", &DataBase::getProperty);

and write julia function which take this class:

function Eg(db::CppTypes.Database, mat::Cint)
    return GetProperty(db, mat)
end

and try to get cfunction pointer on this function from c++:

auto *eg = (double (*)(DataBase *, int)) jl_unbox_voidpointer(jl_eval_string("@cfunction(Eg, Cdouble, (Ptr{Cvoid}, Cint))")); 

Pointer exist, but call this is trow an exception.

where im wrong?

Binded classes wrapped on julia side

mutable struct WorldAllocated <: World
  cpp_object::Ptr{Cvoid}
end

Thanks

[k12Sergey]

Posibly i should change julia signature

function Eg(db::Ptr{Cvoid}, mat::Cint)
    # convert void* to CppTypes.Database ?
    return GetProperty(db, mat)
end

[barche]

Hi,

With cxxWrap I recommend making a function that accepts a SafeCFunction like this:
https://github.com/JuliaInterop/libcxxwrap-julia/blob/d4192fe3ea20829bd399d812863abd8303f9bcab/examples/functions.cpp#L243

The pointer is best generated in Julia, as here in this example:

CxxWrap.jl/test/functions.jl

Line 119 in b1c07f1

c_func = @safe_cfunction(testf, Float64, (Float64,Float64))

[k12Sergey]

Sorry, i still dont get which type should be in c++ signature for binded struct. SafeCFunction know how to handle custom structs?
@safe_cfunction still need to cast into function (which isnt worked)

Is it corect way to get SafeCFucntion from julia?

jlcxx::SafeCFunction *f_data = (jlcxx::SafeCFunction *) jl_unbox_voidpointer(jl_eval_string("@safe_cfunction(testf, Cfloat, (Cfloat, Cfloat))"));

auto f = jlcxx::make_function_pointer<float(float, float)>(*f_data);

This code crash when make_function with what(): Incorrect datatype for cfunction return type, expected Float32 but got Const

[k12Sergey]

I try out to modify example from doc. (original one work correctly)

function Test(eg::CppTypes.Database) :: Cvoid
    println("im test function")
end    
ptr = @safe_cfunction(Test, Cvoid, (Main.CppTypes.DatabaseAllocated,))
println(typeof(ptr))

test_safe_cfunction(ptr)

with the following test_safe_cfunction:

 types.method("test_safe_cfunction", [](jlcxx::SafeCFunction f_data) {
    auto *f = jlcxx::make_function_pointer<void(DataBase* )>(f_data);
    std::cout << f << std::endl;
 });

and it just stop execution, nothing we printed out

[k12Sergey]

Its not obvious how to get jlcxx::SafeCFunction and how to cast it to function with user binded argument.
Is it possible or wrapping work only one way and global variables on julia side should be used? (they very slow and should be const dont check if const will work correctly)

[barche]

I think it should work like this:

function Test(eg::CxxRef{CppTypes.Database}) :: Cvoid
    println("im test function")
end    
ptr = @safe_cfunction(Test, Cvoid, (CxxRef{CppTypes.Database},))
println(typeof(ptr))

test_safe_cfunction(ptr)

 types.method("test_safe_cfunction", [](jlcxx::SafeCFunction f_data) {
    auto *f = jlcxx::make_function_pointer<void(DataBase&)>(f_data);
    std::cout << f << std::endl;
 });

Or if you prefer pointers you can use CxxPtr{Database}. The key is that the types passed to safe_cfunction should all map directly to C types.