Call objc function from c++ world

objc_call.cpp

#if defined(__APPLE__)
#include <objc/message.h>
#include <objc/objc.h>
#include <objc/runtime.h>
template <typename T, typename... Args>
T objc_call(id obj, const char *sel, Args... args) {
    using FuncPtr = T (*)(id, SEL, Args...);
    return reinterpret_cast<FuncPtr>(objc_msgSend)(obj, sel_registerName(sel), args...);
}
template <typename T, typename... Args>
T objc_call(const char *clazz, const char *sel, Args... args) {
    return objc_call<T>(reinterpret_cast<id>(objc_getClass(clazz)), sel, args...);
}
#endif

void test() {
    auto ns_window = glfwGetCocoaWindow(window);
    CFRetain(ns_window);
    auto view = objc_call<id>(ns_window, "contentView");
    CFRetain(view);
    objc_call<void, BOOL>(view, "setWantsLayer:", YES);
    auto layer = objc_call<id>("CAMetalLayer", "layer");
    auto scale_factor = objc_call<CGFloat>(ns_window, "backingScaleFactor");
    objc_call<void, CGFloat>(layer, "setContentsScale:", scale_factor);
    objc_call<void, id>(view, "setLayer:", layer);
    CFRelease(view);
    CFRelease(ns_window);
}