Virtualization in C++ across FFI

Author: tobe2098

include/multipass/logging/log.h

@@ -16,7 +16,9 @@
  */
 
 #pragma once
+#include <iostream>
 
+#include <memory>
 #include <multipass/logging/level.h>
 #include <multipass/logging/logger.h>
 #include <rust/cxx.h>
@@ -45,7 +47,29 @@ Logger* get_logger(); // for tests, don't rely on it lasting
 namespace rust
 {
 void log_message(Level level, ::rust::String category, ::rust::String message);
+class Base
+{
+public:
+    virtual ~Base() = default;
+    virtual void virt_func()
+    {
+        std::cout << "\nBase\n";
+    }
+};
+class Derived : public Base
+{
+public:
+    ~Derived() override = default;
+    void virt_func() override
+    {
+        std::cout << "\nDerived\n";
+    }
+};
+inline std::unique_ptr<Base> get_base()
+{
+    return std::make_unique<Derived>();
 }
+} // namespace rust
 /**
  * Log with formatting support
  *

rxx/rust_logger/src/lib.rs

@@ -18,6 +18,12 @@ pub mod ffi {
         //fn level_from(in_: i32) -> Level;
         include!("multipass/logging/log.h");
         #[namespace = "multipass::logging::rust"]
+        type Base;
+        #[namespace = "multipass::logging::rust"]
+        fn virt_func(self: Pin<&mut Base>);
+        #[namespace = "multipass::logging::rust"]
+        fn get_base() -> UniquePtr<Base>;
+        #[namespace = "multipass::logging::rust"]
         fn log_message(level: Level, category: String, message: String) -> Result<()>;
         //Result<1Type> in a CXX bridge unsafe extern C++ will convert to a try-catch in the C++
         //side which will convert the C++ exception to a rust error.
@@ -37,6 +43,8 @@ fn log_message(level: ffi::Level, category: String, message: String) {
     };
 }
 pub fn log_error(category: String, message: String) {
-    log_message(ffi::Level::error, category, message)
+    log_message(ffi::Level::error, category, message);
+    let mut base = ffi::get_base();
+    base.pin_mut().virt_func();
 }
 fn rust_test_bridge() {}