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use std::ops::Add;
pub trait Encoder {
type Size: Add<Output = Self::Size>;
fn foo(&self) -> Self::Size;
}
pub trait SubEncoder: Encoder {
type ActualSize;
fn bar(&self) -> Self::Size;
}
impl<T> Encoder for T
where
T: SubEncoder,
{
type Size = <Self as SubEncoder>::ActualSize;
//~^ ERROR: cannot add `<T as SubEncoder>::ActualSize` to `<T as SubEncoder>::ActualSize`
fn foo(&self) -> Self::Size {
self.bar() + self.bar()
}
}
pub struct UnitEncoder;
impl SubEncoder for UnitEncoder {
type ActualSize = ();
fn bar(&self) {}
}
pub fn fun<R: Encoder>(encoder: &R) {
encoder.foo();
}
fn main() {
fun(&UnitEncoder {});
}
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