Cocoa Window with Metal layer in pure C++

main.cpp

#include <objc/runtime.h>
#include <objc/message.h>
#include <CoreGraphics/CoreGraphics.h>

template <typename Return, typename... Args> auto send(id obj, SEL selector, Args... args) {
    return reinterpret_cast<Return (*)(id, SEL, Args...)>(objc_msgSend)(obj, selector, args...);
}

template <typename Return, typename... Args> auto send(Class cls, SEL selector, Args... args) {
    return reinterpret_cast<Return (*)(id, SEL, Args...)>(objc_msgSend)(reinterpret_cast<id>(cls), selector, args...);
}

class Window {
public:
    int run() {
        auto application = send<id>(objc_getClass("NSApplication"), sel_registerName("sharedApplication"));
        send<void>(application, sel_registerName("setActivationPolicy:"), 0);

        auto windowDelegate = objc_allocateClassPair(objc_getClass("NSObject"), "WindowDelegate", 0);
        class_addMethod(windowDelegate, sel_registerName("windowWillClose:"), reinterpret_cast<IMP>(windowWillClose), "v@:@");
        objc_registerClassPair(windowDelegate);

        _window = send<id>(objc_getClass("NSWindow"), sel_registerName("alloc"));
        send<void>(_window, sel_registerName("initWithContentRect:styleMask:backing:defer:"), CGRectMake(0, 0, 800, 600), 15, 2, NO);
        send<void>(_window, sel_registerName("setTitle:"), send<id>(objc_getClass("NSString"), sel_registerName("stringWithUTF8String:"), "Cocoa window"));
        send<void>(_window, sel_registerName("center"));
        send<void>(_window, sel_registerName("setDelegate:"), send<id>(windowDelegate, sel_registerName("new")));
        send<void>(_window, sel_registerName("makeKeyAndOrderFront:"), nil);
        send<void>(application, sel_registerName("activateIgnoringOtherApps:"), YES);

        send<void>(send<id>(objc_getClass("NSApplication"), sel_registerName("sharedApplication")), sel_registerName("run"));

        createMetalLayer();

        objc_disposeClassPair(windowDelegate);
        return 0;
    }

private:
    id _window;
    id _metalLayer;

    static void windowWillClose(id self, SEL _cmd, id sender) {
        send<void>(send<id>(objc_getClass("NSApplication"), sel_registerName("sharedApplication")),
                   sel_registerName("terminate:"), nil);
    }

    void createMetalLayer() {
        _metalLayer = send<id>(objc_getClass("CAMetalLayer"), sel_registerName("new"));
        send<void>(_metalLayer, sel_registerName("setDevice:"), send<id>(objc_getClass("MTLCreateSystemDefaultDevice"), sel_registerName("new")));

        send<void>(_metalLayer, sel_registerName("setPixelFormat:"), 70); // MTLPixelFormatBGRA8Unorm
        send<void>(_metalLayer, sel_registerName("setFrame:"), send<CGRect>(_window, sel_registerName("frame")));
        send<void>(_window, sel_registerName("contentView"), sel_registerName("setLayer:"), _metalLayer);
        send<void>(_window, sel_registerName("contentView"), sel_registerName("setWantsLayer:"), YES);
    }
};

int main() {
    Window win{};
    return win.run();
}