Designing a logging abstraction: Go interfaces vs Rust traits

WHAT THIS TESTS It checks whether you can model an abstraction over multiple implementations and explain precisely how each language dispatches the call, including the choice Rust gives you.

A GOOD ANSWER COVERS The abstraction is a single-method contract for writing a log line. In Go you declare type Logger interface { Log(msg string) error } and write file, network, and stdout types each with a Log method; the consumer is func Process(l Logger, msg string) error. Conformance is implicit. In Rust you declare trait Logger { fn log(&self, msg: &str) -> std::io::Result<()>; } and impl it explicitly for each type. You then choose the consumer signature: fn process<L: Logger>(l: &L, msg: &str) uses generics and is monomorphized into static, often inlined calls, while fn process(l: &dyn Logger, msg: &str) takes a trait object and dispatches dynamically through a vtable.

KEY DISPATCH DIFFERENCE Go interface method calls are always dynamic: the interface value carries a type descriptor and pointer, and the call indirects through a method table. Rust defaults to static dispatch via monomorphization when you use generics or impl Trait, paying no runtime indirection; you must explicitly write dyn Trait (typically behind a reference or Box) to get dynamic dispatch. To hold a mixed collection of loggers, Go uses []Logger and Rust uses Vec<Box<dyn Logger>>.

COMMON WRONG ANSWERS Saying Rust traits are always dynamically dispatched. Forgetting that a heterogeneous collection in Rust needs dyn. Claiming Go offers a static-dispatch option for interfaces.

LIKELY FOLLOW-UPS What is object safety and why can not every trait be a dyn? What is the performance cost of a vtable indirection? When would you prefer Box<dyn Logger> over generics?

ONE CONCRETE EXAMPLE Logging to all destinations: in Go, loggers := []Logger{file, net, stdout}; for _, l := range loggers { l.Log(msg) } dispatches each call dynamically. In Rust, let loggers: Vec<Box<dyn Logger>> = vec![Box::new(file), Box::new(net), Box::new(stdout)]; for l in &loggers { l.log(msg)?; } also dynamic, but if you instead wrote a generic function over one concrete logger type, those calls would be statically dispatched and inlinable.