Rust's lambdas are structs containing (references to) exactly the data from the parent scope that their bodies refer to, no more, no less. It's fine for that se

Rust's lambdas are structs containing (references to) exactly the data from the parent scope that their bodies refer to, no more, no less. It's fine for that set to be empty, resulting in an empty, zero-sized value. As we discussed[1] recently, unique types + monomorphisation means that many/most calls of closures (i.e. even ones that capture variables) can compile down to an inlineable static function call. If there's no references to external data in the body, this function call is exactly what you want with a function pointer, except better, because it is not a virtual call. That is, the scheme that Rust and C++11 use for closures automatically gives a better result than passing pointers. (Passing a function value is the same, they have unique types just like closures, but with the ability to be coerced to C-style function pointers.) By the way, function pointers have been able to be passed directly where closures, both the new and old forms, are expected since at least 0.13. [1]: https://news.ycombinator.com/item?id=11054890 https://news.ycombinator.com/item?id=11054890