Define Associated Type of Trait Bound on an Associate Type

help
1

Hi there,

I am not sure if I am phrasing my title correctly. But i.e. I want to know if there is a syntax for achieving the following:

trait InfoProvider {
    type Item;
}

trait First {
     type Info: InfoProvider; 
}

trait Second {
   type GetInfo: First<<Info as InfoProvider>::Item = u32>
}
2

How about this?

trait Second
where
    <Self::GetInfo as First>::Info: InfoProvider<Item = u32>,
{
   type GetInfo: First;
}
2 Likes
3

Thanks for the quick and perfect answer!

4

@alice sorry to bother you again. I have another question regarding "reading" this as the compiler would.

My current understanding is:

The trait Second only exists where its associated type GetInfo adheres to the trait bound.

But although, the trait Second does not exist in another definition and I can not define another trait Second with a less restrictive associated type, I still need to add this trait bound to every impl of

impl<T: Second> .

So do I understand it correctly, that it is rather a shortcoming of syntax and rustc's capabilities to detect that?

5

An impl block must always list all requirements for the impl block to apply.

6

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