Cocoa Window with Metal layer in pure C++

main.cpp

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

auto static constexpr WINDOW_TITLE = "Prototype";
auto static constexpr WINDOW_WIDTH = 1280;
auto static constexpr WINDOW_HEIGHT = 720;

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

template <typename... Args> auto send(char const* cls, char const* selector, Args... args) {
    return send(reinterpret_cast<id>(objc_getClass(cls)), selector, args...);
}

extern id NSDefaultRunLoopMode;

auto static running = true;

class Window {
public:
    ~Window() {
        send(_metalLayer, "release");
        send(_window, "release");
    }

    auto run() -> int {
        send(send("NSApplication","sharedApplication"), "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("NSWindow", "alloc");
        send(_window, "initWithContentRect:styleMask:backing:defer:", CGRectMake(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT), 15, 2, NO);
        send(_window, "setTitle:", send("NSString", "stringWithUTF8String:", WINDOW_TITLE));
        send(_window, "center");
        send(_window, "setDelegate:", send("WindowDelegate", "new"));
        send(_window, "makeKeyAndOrderFront:", nil);
        send(send("NSApplication","sharedApplication"), "activateIgnoringOtherApps:", YES);

        createMetalLayer();

        while (running) {
            send(send(_window, "contentView"), "setNeedsDisplay:", YES);
            id event = send(send("NSApplication","sharedApplication"), "nextEventMatchingMask:untilDate:inMode:dequeue:", ULONG_MAX, nil, NSDefaultRunLoopMode, YES);
            send(send("NSApplication","sharedApplication"), "sendEvent:", event);
        }

        objc_disposeClassPair(windowDelegate);
        return 0;
    }

private:
    id _window;
    id _metalLayer;

    auto static windowWillClose(id self, SEL _cmd, id sender) -> void {
        send(send("NSApplication", "sharedApplication"),"terminate:", nil);
        running = false;
    }

    auto createMetalLayer() -> void {
        _metalLayer = send("CAMetalLayer", "new");
        send(_metalLayer, "setDevice:", send("MTLCreateSystemDefaultDevice", "new"));
        send(_metalLayer, "setPixelFormat:", 70); // MTLPixelFormatBGRA8Unorm
        send(_metalLayer, "setFrame:", CGRectMake(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT));

        auto contentView = send(_window, "contentView");
        send(contentView, "setWantsLayer:", YES);
        send(contentView, "setLayer:", _metalLayer);
    }
};

auto main(int, char**) -> int {
    return Window{}.run();
}