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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Trait with private items

Hi,

I would like to make a trait some items private and some public. I have considered to use sealed super trait, but in my case the private items depend on public ones, so it didn't work (also, I think it would not make private items inaccessible).

I would like something like this:

// The trait should be visible by user and usable in bounds.
// It cannot be implemented by user, but that's fine.
pub trait MyTrait {
    // This type should be public
    type Item;
    
    // This type should be private, it is an implementation detail,
    // completely invisible to user, it should not be a breaking
    // change to change or remove this.
    type Iter: Iterator<Item = Self::Item>;
    
    // This function should be private, it is an implementation detail,
    // completely invisible to user, it should not be a breaking
    // change to change or remove this.
    fn get_item(&mut self) -> Self::Item;
}

// There are functions like this in my library
pub fn do_something<T: MyTrait>(value: T) -> T::Item {
    todo!()
}

// ... and some implementations of MyTrait
struct Foo;
impl MyTrait for Foo { /* ... */ }

I am currently considering two approaches:

• Just #[doc(hidden)] the private items (and maybe add extra unnameable-typed argument to functions).
• Keep them public and document them (maybe adding a "but pretend you do not see this" note).

I don't like any of them. Is there anything better?

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