> At least there is precedence for functions to have magical compiler-ness for 'doing stuff', instead of overloading field access which is one of the simplest operations you can have.
Except we don't actually have precedence for "I'm going to declare a function, but it's not actually implemented in Rust, instead it's a cue to the compiler to do other magical stuff". Lang items are in fact the opposite; they're telling the compiler "here's the implementation for an extension point you've defined". For example the "panic_impl" lang item is a function that's invoked when code panics. The closest I can think of to what you're referring to is the fact that the type identified as "owned_box" has special dereferencing behavior, but that can be modeled as the compiler providing an implementation for an un-namable trait on the owned_box item where the trait represents the new deref behavior (just as how Deref and DerefMut represent the existing deref behaviors).
> tbh, you don't need to know how await works.
You need to know the type in order to determine if `fut.await()` is invoking this magical semantics-altering compiler behavior or if it's just invoking a method that happens to be named `await` (given that the lang_item proposal means await is no longer a keyword).
> Contrast with the field access one and you don't even know its something else entirely.
Except you do, because await is a keyword. It's impossible in Rust 2018 to have a field named await, and so any expression that looks like `x.await` is guaranteed to be an invocation of the await behavior.
> I guess I just don't buy that it can't be a method.
It cannot be a method that is implemented as a call to an intrinsic. The await keyword requires rewriting the function that invokes it.
Except we don't actually have precedence for "I'm going to declare a function, but it's not actually implemented in Rust, instead it's a cue to the compiler to do other magical stuff". Lang items are in fact the opposite; they're telling the compiler "here's the implementation for an extension point you've defined". For example the "panic_impl" lang item is a function that's invoked when code panics. The closest I can think of to what you're referring to is the fact that the type identified as "owned_box" has special dereferencing behavior, but that can be modeled as the compiler providing an implementation for an un-namable trait on the owned_box item where the trait represents the new deref behavior (just as how Deref and DerefMut represent the existing deref behaviors).
> tbh, you don't need to know how await works.
You need to know the type in order to determine if `fut.await()` is invoking this magical semantics-altering compiler behavior or if it's just invoking a method that happens to be named `await` (given that the lang_item proposal means await is no longer a keyword).
> Contrast with the field access one and you don't even know its something else entirely.
Except you do, because await is a keyword. It's impossible in Rust 2018 to have a field named await, and so any expression that looks like `x.await` is guaranteed to be an invocation of the await behavior.
> I guess I just don't buy that it can't be a method.
It cannot be a method that is implemented as a call to an intrinsic. The await keyword requires rewriting the function that invokes it.