Accept uninstantiated struct as func parameter

help
1

Hi Dear Community,

I got some structs which impled Marker Trait, which got the same associated function test().
Is it possible to make a function accept uninstantiated struct as parameter?
So that I can call T::test() directly without instantiation.
like

// this works but bar should be instantiated struct instance. 
fn Foo(bar: T) -> String 
where T: Marker {
    T::test()
}

trait Marker: Sized {
    fn test() -> String;
}

Or any other way I can achieve similar result?
2

You have to define the generic parameter T in Foo, adding the Marker trait bound to it. Then you can call the associated function:

fn Foo<T: Marker>() -> String {
    T::test()
}

trait Marker: Sized {
    fn test() -> String;
}
2 Likes
3

The original code already had a where clause that will do the same thing right?

I think this is a type inference problem. How does foo know what concrete type of T to monomorphize to? The parameter wal doing that in the original code.

I think this is a case for the turbo fish. Assuming you have some struct Bar that is Marker, then you would do something like this: foo::<Bar>(). Rustc can then figure out exactly what type it needs to monomorphize.

4

Yep. When the compiler has no other information it can use to infer the type parameter you'll need to supply it yourself using turbofish.

1 Like
5

The original code didn't have a generic parameter, T was referring to some type named exactly T.

2 Likes
6

Oh yeah, I totally missed that, distracted by the where clause I guess.

7

Thanks a lot!