Is it possible to have a generic function on a trait?

Question

I have:

struct Plumbus<\'a> {
    grumbo: &\'a Grumbo,
}

trait Grumbo {
    fn dinglebop(&self, x: &mut T) -> bool { false }
}


        

Answer 1

Is it possible to have a generic function on a trait?

Yes. But you are then trying to use the trait as an object. If a trait has a generic method then you can't use it as an object, but you can still use it as a bound for a type parameter.

That is, instead of using &'a Gumbo, use a T: Gumbo:

struct Plumbus<'a, T: Gumbo> { 
    grumbo: &'a T,
}

With the trait object, the implementation is only known at runtime. And its generic parameter is part of the implementation type, so the compiler couldn't know how to call it. With T: Gumbo you are putting a constraint on what T can be, but T will always be known by the compiler at the point of use, which includes any parameters of its own.

See also:

• Understanding Traits and Object Safety
• What makes something a "trait object"?