Comment by amelius
10 hours ago
Closures are the bread and butter of functional programming, but Rust made closures a complicated mess.
10 hours ago
Closures are the bread and butter of functional programming, but Rust made closures a complicated mess.
Closures are a complicated mess. Functional programming languages hide the mess with garbage collection.
This isn't the right framing IMO. Closures actually aren't complicated with GC for the same reason structs with references aren't complicated, at least as far as the programmer is concerned. You could say functional languages "hide the mess" there too, but even if you take that perspective, it's nothing to do with closures in particular. Closures are just one of the things that need memory, and memory management is tricky without GC.
If you understand the borrow checker, closures are just not that much on top of things.
In fact I can’t remember the last time I had to fight with them.
I really wanted just yesterday to create a dyn AsyncFnMut, which apparently still needs async-trait to build the stable. but I was pretty much unable to figure out how to make that work with a lambda. saying this is all trivial once you understand the borrow machinery is really understating it.
> saying this is all trivial
The comment above isn't saying that closures are trivial. Once you understand the borrow checker, you understand that it's a miracle that closures in Rust can possibly work at all, given Rust's other dueling goals of being a GC-less language with guaranteed memory safety despite letting closures close over arbitrary references. Rust is in uncharted territory here, drawing the map as it goes.
Async is the stuff that messes up everything. Closures are not complicated.
Well... Rust is not a functional language, so it is not surprising that its closures are complicated.