Description
It started with this error:
pub trait VideoDriver {
static fn init() -> Self;
}
pub trait Platform {
static fn init<D: VideoDriver>() -> Self;
static fn foo() -> bool;
}
pub fn run<P: Platform, D: VideoDriver>() {
let platform: P = Platform::init::<D>();
}
---------------------------------------------------------------------------------------------
trait_generic_method.rs:11:19: 11:38 error: not enough type parameters provided for this item
trait_generic_method.rs:11 let platform: P = Platform::init::<D>();
^~~~~~~~~~~~~~~~~~~~~~
trait_generic_method.rs:11:19: 11:38 error: cannot determine a type for this bounded type parameter: unconstrained type
trait_generic_method.rs:11 let platform: P = Platform::init::<D>();
^~~~~~~~~~~~~~~~~~~~~~
Which is confusing because the init() method is just defined on one type parameter.
However if I change the line to let platform: P = Platform::init::<P, D>(); it compiles, which is confusing for the same reasons.
The cause for this is that you can specify the type of an trait impl by appending an ::<T> to the call of an function like this: let is_foo = Platform::foo::<int>(), which is fine as long as the function itself has no specific trait bounds. Combined though it's a mess, as it's not even clear in which order the parameters go.
As the type selection really belongs to the trait, and not to an function of that trait, I propose that the syntax should get changed to let platform = Platform::<P>::init::<D>().
More linenoise, but at least it's not confusing.