How so? This feel distinct from the "algebraic effects"-like features like constness, async, can-panic, can-unwind, etc., since this is a property of the types themselves rather than of functions.
How so? This feel distinct from the "algebraic effects"-like features like constness, async, can-panic, can-unwind, etc., since this is a property of the types themselves rather than of functions.
The traits are essentially effect handlers for effects like `drop<T>`, `move<T>`, `forget<T>` which are implicitly charged to the a function which owns a `T` and does drops, moves, or forgets it.
Inferring the capabilities of the function from the traits of the types of the arguments is similar to tracking effects. The function charges `drop<T>` when `x: T` goes out of scope, which is handled by the trait implementation. If Rust had a proper algebraic effects type system, you would be able to see this directly in the signature of the function (and even more, if the trait impls themselves had their effects tracked, you'd be able to see from the signature of the function the side effects of deallocation of its owned variables, like if `drop<File>` performs `io`).
I haven't seen any algebraic effects system that is that powerful
The closest is linear types but even then drop isn't an effect but also a function you can call to allow not continuing the references
Yeah I should have phrased that better. The traits themselves are not the effects, they're bits of code which can have side effects. Rust doesn't track those side effects in the type system yet, but !Forget especially is the essence of that idea. If you implement it for everything owned by a function, you can basically infer that the function does not have the leak effect (which would be an effect in the effect row of a Forget trait implementstjon).
If you try treat memory as an effect you gain the need for several polymorphic effect type functions drop, forget, etc which map a type to the effect row charged by its corresponding Drop, Forget impl. Rust doesn't have that type system obviously.