# object type unsoundness

## `boluo-core 0.4.1`

also affects
- `boluo 0.5.3`

`(dyn AnyService<Req, Error = Err, Response = Res> + 'static): AnyService<Req>`

pub trait Service<Req>: Send + Sync {
    type Response;
    type Error;
    // ...
}

trait AnyService<Req>: Send + Sync {
    type Response;
    type Error;
    // ...
}

impl<S, Req> AnyService<Req> for S
where
    S: Service<Req> + ?Sized,
{
    type Response = S::Response;
    type Error = S::Error;
    // ...
}

## `daab 0.4.0`

`(dyn Builder<Rc<(dyn std::any::Any + 'static)>, Rc<(dyn std::any::Any + 'static)>, Artifact = test_dyn::ComplexNode, DynState = (), Err = never::Never> + 'static): rc::Builder`

pub trait Builder: Debug + 'static {
	type Artifact : Debug + 'static;
	type DynState : Debug + 'static;
	type Err : Debug + 'static;
    // ... 
}

pub trait SimpleBuilder: Debug + 'static {
	type Artifact : Debug + 'static;
    // ... 
}

impl<B: ?Sized + SimpleBuilder> Builder for B {
	type Artifact = B::Artifact;
	type DynState = ();
	type Err = Never;
}

## `flipflop 0.1.0`

`(dyn AccumObj<Item = <A as Accum>::Item> + 'a): AccumObj`

pub trait AccumObj {
    type Item;
}
impl<A: ?Sized + Accum> AccumObj for A {
    type Item = A::Item;
}
pub trait Accum {
    type Item;
    // ...
}

## `thirtyfour 0.34.0`

Also affects

- https://github.com/Bubbler-4/gaboja `gaboja 0.4.1`
- https://github.com/DedicatedSoftwareDev/Web-bot-with-Rust
- https://github.com/JohannesNicholas/rust-chess-scraper
- https://github.com/Kirloxious/wordle-solver
- https://github.com/Sw1ndlers/ChromedriverManager `chromedriver-manager 0.3.5`
- https://github.com/benfrankel/find_a_job
- https://github.com/evshary/parse_sheet_from_weixin

`dyn ElementQueryFn<T, Fut = Pin<Box<dyn Future<Output = Result<T, WebDriverError>> + Send>>>: types::ElementQueryFn<T>`

pub trait ElementQueryFn<T>: Send + Sync {
    type Fut: Future<Output = WebDriverResult<T>> + Send;
}

impl<T, Fut, Fun> ElementQueryFn<T> for Fun
where
    Fun: Fn(WebElement) -> Fut + Send + Sync + ?Sized,
    Fut: Future<Output = WebDriverResult<T>> + Send,
{
    type Fut = Fut;
}

`dyn ElementQueryFn<T>` does not implement `Fn(WebElement)`

## `transmutter`

Oh look at me, I am so funny, publishing a crate for safe transmute

pub trait Transmutter<U> {
    type Target;
}

impl<T: ?Sized, U> Transmutter<U> for T {
    type Target = U;
}

fn transmutter<T: ?Sized, U>(source: <T as Transmutter<U>>::Target) -> U {
    source
}

pub fn transmutte<T, U>(value: T) -> U {
    transmutter::<dyn Transmutter<U, Target = T>, U>(value)
}

## `hooks-yew` / `hooks`

oh no, a lifetime error on a call to `erased_use_hook` for `dyn for<'a> ErasedHook<(&'a Props,), ValueGat = dyn for<'hook> ValueGat<'hook, Value = VNode>>`

https://github.com/frender-rs/hooks/blob/7d4127130725e1eb347c05d6460a15dd59c89670/packages/hooks-core/src/erased_hook.rs

the underlying pattern is as follows:

trait Trait<T> {
    fn method(&self);
}
trait Erased<T> {
    type Assoc;
    fn erased(&self);
}
impl<T> Trait<T> for dyn Erased<T, Assoc = ()> {
    fn method(&self) {
        self.erased();
    }
}
impl<T, H: Trait<T> + ?Sized> Erased<T> for H {
    type Assoc = ();
    fn erased(&self) {
        self.method();
    }
}

fn break_me(hr: Box<dyn for<'a> Erased<&'a (), Assoc = ()>>) {
    // `hr` implements `for<'a> Erased<&'a ()>` via the builtin impl
    //
    // using the indirection via `dyn Erased<T>: Trait<T>` forces
    // `'a` to not be higher-ranked.
    hr.erased();
}