dynamic use dll or so file error!

[master]

I want to access dynamic libraries on different platforms, but I 
still can not get the function, so do not write it? Where is 
wrong?

import core.runtime;
import std.stdio;
import std.string;
version(Windows)
{
        import std.c.windows.windows;
}
else version(Posix)
{
        import core.stdc.stdio;
        import core.stdc.stdlib;
        import core.sys.posix.dlfcn;
}

void* getSymbolAddress(void* handle, string name)
{
        version(Windows)
    {
        FARPROC proc = GetProcAddress(cast(HMODULE)handle, 
name.ptr);
        if (proc is null)
        {
                        writefln(": can't resolve symbol "~name);
                        return null;
        }
        return cast(void*)proc;
    }
        else version(Posix)
    {
        auto cstr = toStringz(symbol);
        return dlsym(handle, cstr);
    }
}

struct Binder(T)
{
        void opCall(string name, void* lib)
        {
                *fptr = getSymbolAddress(lib, name);
                writefln("111111111111111111111"~name);
        }
        private void** fptr;
}

template bindFunc(T)
{
        Binder!(T) bindFunc(inout T a)
        {
                Binder!(T) res;
                res.fptr = cast(void**)&a;
                return res;
        }
}

extern (C)
{
        void function() net_tcp_send;   
}

void LoadPlatform(void* lib)
{
        bindFunc(net_tcp_send)("net_tcp_send", lib);
}

int main()
{
        void* hp  = Runtime.loadLibrary("ShuNet.dll".dup);
    if(hp is null)
    {
        writefln("error loading ShuNet.dll");
        return 1;
    }
        writefln("ShuNet.dll is loaded");

        LoadPlatform(hp);
                
        printf("net_tcp_send=>%p", net_tcp_send);

        net_tcp_send(); // this error

        if(!Runtime.unloadLibrary(hp))
    {
                writefln("error freeing ShuNet.dll");
        return 1;
    }
    writefln("End...");

    return 0;
}