This example uses metal-cpp and a couple of additions to metal-cpp-extensions in order to show a pure C++ GLFW / Metal implementation. It's really a port of this Objective-C based example.
The metal-cpp-extensions code was taken from this Apple sample and a couple of methods were added to NS::Window and NS::View to allow Metal to be set-up, as this code does not use MetalKit.
Note that Apple do not support metal-cpp-extensions and there are a couple of extensions that have been made to it, however it's pretty simple to extend yourself.