But you’re also missing one use of the impl keyword: fn func() -> impl Trait.
[…] So dropping the impl in [return position] might not be completely impossible like the other uses of impl.
But the impl markes that it is a trait to the programmers.
Take the following functions:
func1()->A{...}
func2()->A{...}
Does the following snippet compile?
let mut thing = func1();
thing = func2();
Under the current rules we know it will. But if A could be a trait, the functions could return different types. We currently mark that with the impl.
Why? What value does -> () provide? Why not elide that?
What value is provided by keeping it?
What value does cluttering up your code with -> () provide?
Why a syntactic special-case for exactly that type and not any other random type?
Because the unit type is special, just like the never ! type. () also has the special importance of being the return value of an empty statement and some other stuff.
languages w/o [semicolons] feel awkward since you’re generally limited to one statement per line
But the impl markes that it is a trait to the programmers.
Take the following functions:
func1()->A{...} func2()->A{...}Does the following snippet compile?
let mut thing = func1(); thing = func2();Under the current rules we know it will. But if A could be a trait, the functions could return different types. We currently mark that with the
impl.What value does cluttering up your code with
-> ()provide?Because the unit type is special, just like the never
!type.()also has the special importance of being the return value of an empty statement and some other stuff.It’s fixed with semicolons ;-)