FFPointer-Bridging-Header.h

int invoke_fun(int (*f)(void));

invoke_fun.c

#include "invoke_fun.h"

int invoke_fun(int (*f)(void)) {
    return f();
}

invoke_fun.h

#ifndef __SwiftTestApp__invoke_fun__
#define __SwiftTestApp__invoke_fun__

int invoke_fun(int (*f)(void));

#endif

main.swift

import Darwin
import Foundation

let handle = dlopen("/usr/lib/libc.dylib", RTLD_NOW)
let sym : UnsafeMutablePointer<Void> = dlsym(handle, "random")
let rawPointer = UnsafeMutablePointer<() -> Int32>(sym)
let opaquePtr : COpaquePointer = COpaquePointer(rawPointer)
let cFunPointer  = CFunctionPointer<() -> Int32>(opaquePtr)
println(invoke_fun(cFunPointer))